Method and instrument for measuring bead cutting shape of electric welded tube

ABSTRACT

To precisely measure bead cutting shapes of electric resistance welded pipes without being affected by difference in luminance level between cut and uncut portions in optical cutting images, an image is obtained by overlaying an optical cutting image with the optical cutting image subjected to thinning processing. A profile of the welded pipe is approximated with a quadratic function and a region containing the bead apex coordinates is identified as the bead. Shape data of the pipe surface at the portion corresponding to the bead portion is obtained from the preset left and right boundaries of the bead portion and the apex position of the separately-calculated bead portion, and bead width, height, slope angle, and unevenness at the left and right boundaries between the bead portion and base pipe portion, are each calculated, based on the left and right bead shape approximation functions and base pipe shape approximation function.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and device for measuringwelded bead cutting shapes in electric resistance welded pipes,including the position of the bead.

2. Description of the Related Art

In general, electric resistance welded pipes, such as electricresistance steel pipes, are manufactured by continuously forming steelplates or steel coils into a tubular form, and continuously performingbutt welding both sides of the steel coil in the longitudinal directionby means such as high-frequency induction heat-pressure welding orresistance heat-pressure welding.

A raised portion called a “bead” is formed at the weld portion of theelectric resistance welded pipe due to the butt welding, on the insideof the pipe and the outside of the pipe. Generally, the bead iscontinuously cut in the longitudinal direction of the steel pipe by acutting tool on the production line further downstream from the welder.The shape of the surface of the pipe after the bead portion has been cutoff (hereafter referred to as “bead cutting shape”) preferably becomesone with the outline shape of the pipe other than the weld, such thatwhere the bead was cannot be distinguished, ideally. In order to achievethis, the cutting tool tip must be held at an appropriate position onthe surface of the electric resistance welded pipe.

Conventionally, a worker has measured the bead cutting shape, visuallyor using a micrometer or the like, at the time of starting cutting, andadjusted the cutting tool to the optimal position. However, there havebeen cases wherein, while manufacturing a number of electric resistancewelded pipes, the position of the cutting tool shifts due to a varietyof reasons, the blade of the cutting tool is nicked, etc., causingdefective cutting such as not all of the bead being cut off of theelectric resistance welded pipe product or cutting too deep. Suchcutting defects not only mar the look of the electric resistance weldedpipe product; using electric resistance welded pipes with cuttingdefects for piping subjected to pressure such as gas lines or the likemay place the pipe at risk of rupturing.

Accordingly, there is the need to measure and monitor the bead cuttingshape while manufacturing, and suitably correct the cutting toolposition or replace the cutting tool with a new one, according to theresults thereof.

Even with regard to the outer face of the pipe which is readily observedfrom the outside, monitoring of the bead cutting shape has to depend onvisual observation of workers, so precision and reproducibility thereofis insufficient, and there have been quantitative and reliabilityproblems.

With regard to the inner face of the pipe, the bead cutting portioncannot be directly observed during manufacturing, due to theconfiguration of the production line. Accordingly, the end portion ofthe pipe is observed at the process where the pipe is cut at the endposition of the line. Alternatively, the line is stopped to cut out asample of the bead position of the pipe by gas cutting, and the innerface is observed. With the former method, the observation position isseveral tens of meters downstream from the cutting position, so therehas been a problem in that in the event that an abnormality occurs inthe cutting, the defective pipe becomes longer until detected, resultingin decrease in yield. Also, with the later method, the cutting toolseizes due to friction heat in the event that the line is stopped, sothe cutting tool must be retracted. Resetting the cutting tool andrestarting the line creates a step between the previously-cut beadcutting shape and the new cutting shape, so that portion is unusable asa product. There has been the problem that productivity decreases due tostopping the line for taking the sample. Only a part in the longitudinaldirection of the product can be inspected in both of the above-describedmethods, so there has been the problem that the quality cannot beguaranteed for the entire length of the product.

In order to solve these problems, a bead cutting shape measurementmethod using the optical cutting method has been proposed. Examples ofthe optical cutting method are disclosed in Japanese Unexamined PatentApplication Publication No. 57-108705 and Japanese Examined PatentApplication Publication No. 60-1138. As shown in FIG. 13, slit light 121from a light source 120 is cast on a measuring object (electricresistance welded pipe 110), and this is observed from a different anglewith a camera 130, thereby observing a slit image (optical cuttingimage) deformed following the surface shape of the measuring object 110.The shape of the object can be calculated from this optical cuttingimage and the geometric position of the observation optical system. Thisis advantageous in that the observation optical system is simple, thatthe measurement sensitivity can be widely changed according to thegeometric placement of the observation optical system, and so forth. Theregion outside of the irradiation region of the slit light is called“background texture”.

Japanese Unexamined Patent Application Publication No. 52-96049 proposesa bead shape observation method wherein an uncut weld bead portion isobserved with the optical cutting method, and marks corresponding to anenlargement ratio determined by optical placement on a display monitor140.

However, these methods only display a measurement image. Judgment of thebead cutting shape is performed by workers visually judging the monitor140, and automatic measurement is not yet employed.

An example of a determination method for automatic measurement is thetechnique disclosed in Japanese Patent No. 2618303, for example.According to this, a method is proposed wherein a picture is taken ofthe steel pipe bead cutting portion using an optical cutting image fromslit light and an ITV camera at the time of measuring the shapefollowing cutting the welding bead of the electric resistance weldedpipe, and as shown in FIG. 13, the cross-sectional shape is calculatedby performing thinning processing (taking a region wherein one pixel isconnected in one direction as a thin line) on the cross-sectional shapepicture, the cut portion and uncut portion are distinguished by theluminance of the cross-sectional shape, the value for the center of thedistinguished cut portion and the value at the right edge of the cutportion and the value at the left edge of the cut portion are obtained,and the cutting depth, and amount of cutting inclination are calculatedbased on these three calculated values.

However, with the technique disclosed in Japanese Patent No. 2618303,the specific method for thinning processing only involves performingcomputation for directly substituting luminance to Y-axial coordinates,such as plotting the maximum luminance in a direction parallel to thepipe axis (Y-axial direction) obtained from the optical cutting imageonto the coordinates on an X axis extending in the circumferentialdirection of the pipe (this is equivalent to the width direction formaterial steel plates and steel coils, and accordingly with hereafter bereferred to as the width direction), so there is the problem in thatthere are cases wherein an accurate cross-sectional shape cannot beobtained.

Describing this in detail, from the experience of the Inventorsrepeating experiments at the manufacturing site, while the surface ofthe cut portion of the electric resistance welded pipe immediatelyfollowing cutting has a specular surface, the surrounding uncut portionsare blackish due to an oxide layer adhering thereto, so the degree ofdiffusion of the slit light thereof differs. Accordingly, the luminanceof the optical cutting image of the bead cutting portion is notnecessarily around the same degree in the width direction. For example,there are cases such as in FIG. 14 wherein almost all of the slit lightof the cut portion exhibits specular reflection (reflection in theopposite direction to the incident direction at the same angle as theincident angle), with the luminance thereof being one-tenth or less thanthat of the uncut portion. This is due to the fact that in the eventthat the incident angle and the reception angle differ, such specularreflection light actually appears to have less luminance.

In such cases, the optical cutting image becomes lost in noise, so thebead cutting shape cannot be obtained well. Attempting to raise theluminance of the cut portion by raising the gain or extending theexposure time of the observation optical system of the ITV camera or thelike leads to exceeding the range of the maximum luminance of thespecifications of the observation optical system such as theaforementioned camera or the like (halation) at the uncut portion asindicated by (c) in FIG. 1, so the shape of the uncut portion cannot beaccurately distinguished. The reason is that in the event that suchexceeding of the range of luminance occurs, multiple pipe axis directioncoordinates (Y-axial coordinates) indicating the maximum luminanceappear at the uncut portion on the optical cutting image, and the pipeaxis direction coordinates (Y-axial coordinates) indicating the maximumluminance cannot be uniquely determined.

The present invention has been made to solve the problems such asdescribed above, and accordingly, it is an object thereof to provide amethod and device for precisely measuring the bead cutting shape ofelectric resistance welded pipe without being affected by the differencein luminance level between the cut portion and uncut portion in opticalcutting images.

With regard to suppressing the effects of noise in such an opticalcutting method, proposals in other fields using the optical cuttingmethod are conventionally known.

Japanese Unexamined Patent Application Publication No. 57-208404proposes a method wherein an optical cutting image is searchedvertically from top to bottom and an optical cutting line is extractedonly from within a section wherein a portion greater than apredetermined setting value first occurs, and subsequent extraction ofoptical cutting lines is terminated at the one scanning line, therebypreventing erroneously detecting abnormal reflections at portions of theoptical cutting line on the object other than the slit luminescent lineposition.

Also, Japanese Unexamined Patent Application Publication No. 2-35306proposes a shape detecting method wherein the entire region of theacquired optical cutting image is scanned in the direction crossing theoptical cutting line, and in the event that there is a peak value due tothe noise image on the scanning line, an optical cutting search range isset based on the optical cutting line position detected on the samescanning line over the entire screen, thereby ignoring noise.

Also, Japanese Unexamined Patent Application Publication No. 4-240508proposes a three-dimensional shape recognition device for calculatingcoordinates of an object of measurement based on an optical cuttingimage, and judging the image to be an unreal image in the event that theshape thereof exists in a needle-like shape separated from surroundingimages, thereby ignoring that data and recognizing the shape.

However, with the method disclosed in Japanese Unexamined PatentApplication Publication No. 57-208404, a fixed threshold V1 is used forrecognizing the only optical cutting extraction section, so applicationthereof to measuring bead cutting shapes wherein the luminance of theoptical cutting line of the acquired optical cutting image changesgreatly between the cut portion and uncut portion is impossible, asalready described.

Also, the method disclosed in Japanese Unexamined Patent ApplicationPublication No. 2-35306 assumes that parts having raised shapes with agenerally uniform size in the longitudinal direction are arrayed in thedirection of the slit light at equal intervals, as with solderedportions of electronic parts, and generation of noise is explained asbeing secondary light due to reflected slit light off of a neighboringpart, so this is clearly inapplicable to the problems of the presentinvention since a similar noise generation state is not generated at thecut portion of an electric resistance welded pipe.

Also, with the technique disclosed in Japanese Unexamined PatentApplication Publication No. 4-240508, in the state that the opticalcutting image of the cut bead becomes non-continuous at a step portion,the step portion is erroneously recognized as a non-continuous image(unreal image) and ignored, so there has been the problem that thiscould lead to missing cutting defects.

That is to say, no method has yet been found in the Technical Field ofthe Present Invention or the field of shape recognition techniques byoptical cutting in other Technical Fields, for accurately measuring weldbead cutting shapes even in the event that the SN ratio between theoptical cutting line image and the surroundings deteriorates.

The present invention has been made to solve the above-describedproblems, and accordingly it is an object thereof to provide ameasurement method and measurement device which can readily recognizeimage processing abnormality portions due to deterioration in the SNratio in three-dimensional shape measurement by the optical cuttingmethod as being uneven portions due to cutting.

With conventional inventions relating to steel pipe welding beaddetection methods or devices, mechanical methods, methods using eddycurrent sensors, optical methods, and so forth, have been proposed.

(Patent Document 1)

Japanese Examined Patent Application Publication No. 59-2593

(Patent Document 2)

Japanese Unexamined Patent Application Publication No. 2000-176642

(Patent Document 3)

Japanese Unexamined Patent Application Publication No. 5-133940

(Patent Document 4)

Japanese Unexamined Patent Application Publication No. 5-18904

(Patent Document 5)

Japanese Unexamined Patent Application Publication No. 9-72851

(Patent Document 6)

Japanese Unexamined Patent Application Publication No. 60-135705

As for a mechanical method, Patent Document 1, for example, proposes amethod for detecting deviation of the outer face weld portions of therunning pipe using contact-type rollers.

Also, as for a method using a eddy current sensor, Patent Document 2proposes a center position detection method for the welding bead whereina detecting head comprising a magnetic core, performing uniform circularmotion on a concentric axis within a transmission coil and receptioncoil disposed in a concentric cylindrical fashion, is erected above thewelding bead and brought into close proximity, and at the time of themagnetic core passing over the welding bead, passage timing is detectedtwice per rotation of the magnetic core based on the change in impedanceof the reception coil, with the time passing between these passagetimings being computed and compared, thereby detecting the centerposition of the welding bead.

Also, Patent Document 3 proposes a method wherein a plurality of eddycurrent sensors are disposed in a form generally extending in onedirection, and scanning the object of detection by sequentiallyswitching the roles of the eddy current sensors between magnetization,induced-magnetization, and detection, thereby detecting the beadposition from the detection waveform.

Also, as for optical methods, methods have been proposed such as themethod disclosed in Patent Document 4 wherein an image of the surface ofthe pipe is taken and signal waveform features inherent to the weldportion and base metal are extracted and checked against features storedbeforehand so as to distinguish these, or a steel pipe welding beaddetection method such as disclosed in Patent Document 5 wherein a steelpipe is rotated in the circumferential direction and an image is takenof the surface of the pipe with an ITV camera or the like whileirradiating sector light on the surface of the pipe or irradiatingsector light consisting of a point light being scanned, the picturesignals are subjected to noise removal and tilt correction and the liketo form an image which is subjected to correction processing, followingwhich circular arc application is used wherein the difference between acircular arc image to which a circular arc has been applied and anactual image is obtained based on the corrected image, and in the eventthat the difference data exceeds a preset threshold value, judgment ismade that to be a welding bead, while also checking against a tolerancerange for the welding bead width set beforehand for a width rangeexceeding the threshold value, thereby determining the bead position.

Also, Patent Document 6 proposes a bead shape automatic measuring deviceas a common welding bead position and shape automatic measurementtechnique, wherein an image is taken of the welding bead from above andfrom the side, analog image information from the image-taking unit isconverted into grayscale level digital information, and the width andheight and the like of the welding bead is detected based on the digitalimage information.

However, with the method using the contact-type sensor such as disclosedin Patent Document 1, the height of the bead must be approximatelyconstant in the longitudinal direction with the irregularities in heightthereof being relatively steep, so in the event that the irregularitiesin height of the bead is constantly smooth, in the event that the beadheight is low, or in the event that the bead height is not constant inthe longitudinal direction, accurate detection cannot be made.

Also, with the method using the concentric motion magnetic core withinthe concentric cylindrical coils disclosed in Patent Document 2, in theevent that a twisted portion in the seam passes through the detectiondevice position while transporting the electric resistance welded pipewhich is the subject, or in the event that meandering occurs therein,the positional relation between the electric resistance welded pipewhich is the subject and the concentric cylindrical coils or theconcentric motion magnetic core which make up the detection device isoffset, so accurate welding bead position detection cannot be performed.

Also, the method disclosed in Patent Document 3, wherein magnetization,induced-magnetization, and detection coils are disposed generally in onedirection, readily responds to foreign material adhering to the surfaceof the pipe and irregularities and so forth in the height of the surfaceof the pipe besides the bead, so it is difficult to avoid erroneousdetection, and also, in the event of dealing with various sizes such aswith electric resistance welded pipes, multiple detecting heads must beprepared to handle the difference in shape thereof, which increasesmanufacturing costs.

Also, as for a common problem with these eddy current methods, there isthe problem that separate shape measurement means must be provided forevaluating the shape of the welding bead regarding which positiondetection has been performed, increasing the manufacturing costs of thedevice.

In comparison with the above-described methods, the optical methods suchas disclosed in Patent Document 4 and Patent Document 5 allownon-contact detection, and are advantageous in that not only beadposition detection but also bead shape evaluation can be made with thesame device configuration. However, there have been various problems inthe above-described conventional optical methods.

That is, with the method disclosed in Patent Document 4 forweld-portion/base-metal features extraction, primary methods involvedetecting the difference in brightness of the bead portion and otherportions (base metal: hereafter referred to as “base pipe”), but thebrightness (luminance) of the bead portion greatly depends on thewelding conditions and the thickness of the base pipe, so besidedifficulty in obtaining stable detection, there has been the problem ofcases wherein bead recognition cannot be performed in the event that theluminance of the bead portion is low, in particular.

Also, with the steel pipe rotation circular arc application methoddisclosed in Patent Document 5, the steel pipe must be rotated in thecircumferential direction, but at the welding stage of the electricresistance welded pipe, the steel pipe is often connected to the steelcoil which is the base metal, making rotation impossible, and inaddition to this problem, two circular arcs are calculated from fourpoints of data at the image processing stage, so even in the event thatnoise processing is carried out, this method is readily affected byjagged shapes often observed in image data, so there is the problem thaterror readily occurs in the bead position that is calculated, andfurther, the roundness of the electric resistance welded pipe which isthe subject is seldom poor, so there has been the problem that there isa limit to suppressing occurrence of detection error with this methodwhich uses the geometrical principle of a circle wherein the center ofthe pipe exists on a perpendicular bisector of two points.

Also, with the camera image-taking method in Patent Document 6, a pointwhere the gradiation for one line of image rapidly changes is searchedas the method for determining the bead position, so there has been theproblem that in the event that the luminance of the bead portion is low,or depending on the surface properties, there are cases wherein the beadposition cannot be determined.

Further, besides these detection methods, as described in PatentDocument 5, one skilled in the art would readily conceive a method formeasuring the profile of the surface of the steel pipe including thebead position, using an optical cutting method or an optical distancemeasurement method, and detecting the bead position by processing theprofile data. However, in this case, some sort of derivation processingassuming that sudden changes occur in the profile at the bead portionwould be commonly applied as a method for processing the profile data,but advances in welding technology in recent years have led to smoothslopes on the bead, while such derivation processing accentuates minutenoise which readily occurs in optical profile measurements, so detectionof the bead position actually becomes more difficult.

The present invention has been made to solve the problems of theconventional art described above, and it is an object thereof to providea method and device for accurately detecting the bead shape from theshape data of electric resistance welded pipes with the so-calledoptical cutting method detected by slit light or point light scanning,without effects of luminance or profile data noise.

Also, as for an optical method, as disclosed in Patent Document 7, ametal flow angle measurement method for electric resistance welded pipeshas been proposed, wherein slit light is irradiated before bead cuttingon a base pipe which is moving and the optical cutting profile obtainedthereby is optically received as image, the width and height of the beadat the welded portion is detected from the obtained optical cuttingprofile reception signals, and the metal flow angle of the weldedportion is computed based on the detection values of the width andheight of the bead thus obtained.

(Patent Document 7)

Japanese Examined Patent Application Publication No. 60-7586

Also, Patent Document 8 proposes a metal flow angle measurement methodfor the welded portion of electric resistance welded pipes, wherein slitlight is irradiated before bead cutting on a base pipe which is movingand optical cutting profiles each obtained thereby are opticallyreceived as an image, the surface position of the bead corresponding toa predetermined height within the range of ¾ to ⅓ of the maximum heightof the bead based on the rising position of the beard at the weldedportion is detected from the obtained optical cutting profile imagereception signals, and the metal flow angle of the welded portion iscomputed based on the horizontal distance from the slope of the bead onthe surface and the predetermined height thereof, corresponding to thepredetermined height thus obtained.

(Patent Document 8)

Japanese Examined Patent Application Publication No. 60-25234

However, in the event of using a contact-type roller such as disclosedin Patent Document 1 and a speedometer together, the height of the beadmust be approximately constant in the longitudinal direction with theirregularities in height thereof being relatively steep, so in the eventthat the irregularities in height of the bead is constantly smooth, inthe event that the bead height is low, or in the event that the beadheight is not constant in the longitudinal direction, there has been theproblem that accurate detection cannot be made.

Also, with Patent Document 7, the shape of the welding bead is taken asbeing a trapezoid in form, with the relation between the width andheight ratio thereof and the metal flow angle being calculated by ashape index computation circuit based on experiment expressions, butadvances in welding technology in recent years have led to smooth slopeson the bead, and the optimal slope angle changes depending on thethickness of the plate or the usage, so there has been the problem thatoperating while experimentally switching over the calibration curve foreach case becomes extremely troublesome.

Also, with the Patent Document 8, bead width information is used at ¾and ⅓ of the bead height, so in addition to the aforementioned problems,there has been the problem that in the event that the bead shape is offof a triangular shape or trapezoid shape, e.g., in the event that theportion of ⅓ through ¾ of the height is vertical, the denominator of themetal flow computation is zero, the computation results are abnormal.

Also, a method may be conceived wherein the cross-sectional-directionshape (in the direction perpendicular to the axis) of the pipe includingthe weld bead portion is detected and the bead position and slope angleis calculated by derivative values thereof, but in the event that thereis noise on the detected shape data, this is accentuated by thederivation computations of such a method, leading to the problems oferroneous bead shape detection or increased error in the slope anglecalculations.

The present invention has been made to solve the problems in theconventional art as described above, and it is an object thereof todetect bead shapes with precision from the shape data of electricresistance welded pipes detected by the optical cutting method.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide ameasurement method and device for bead cutting shapes which enablehighly precise measurement and detection in manufacturing of electricresistance welded pipes.

According to a first aspect of the present invention, a measurementmethod for a bead cutting shape of an electric resistance welded pipe,for measuring the shape following cutting a bead generated on the innerface or outer face of an electric resistance welded pipe at a weldingportion, comprises: a step for obtaining an optical cutting image bytaking an image of slit light irradiated on the bead portion withimage-taking means, from an angle different to the irradiation directionof the slit light; a step for obtaining each of maximum luminance in thepipe axial direction at a given width-direction coordinate on theoptical cutting image, and maximum luminance in background textureregion outside of the irradiation range of the slit light; a step forperforming interior division of the maximum luminance of the pipe axialdirection and the maximum luminance of the background texture region bya ratio determined beforehand, and setting the obtained luminance as athreshold value; a step for taking a luminance greater than thethreshold value and a weighted mean of pipe axial direction coordinatesindicating the luminance as pseudo-cross-sectional direction coordinatesfor the width-direction coordinates and pipe axial directioncoordinates; and a step for calculating the bead cutting shape of theelectric resistance welded pipe based on a pseudo-cross-sectional shapeobtained by stringing pseudo-cross-sectional direction coordinates inthe width direction, and a predetermined conversion expressiondetermined from a geometric positional relation of the light source ofthe slit light, the image-taking means, and the electric resistancewelded pipe.

According to a second aspect of the present invention, a measurementmethod for a bead cutting shape of an electric resistance welded pipe,for measuring the shape following cutting a bead generated on the innerface or outer face of an electric resistance welded pipe at a weldingportion, comprises: a step for obtaining an optical cutting image, bytaking an image of slit light irradiated on the bead portion withimage-taking means, from an angle different to the irradiation directionof the slit light; a step for taking, in the event that the maximumluminance in the pipe axial direction at a given width-directioncoordinate on the optical cutting image is equal to or exceeds apredetermined fixed threshold value, a weighted mean of pipe axialdirection coordinates indicating the luminance as pseudo-cross-sectionaldirection coordinates for the width-direction coordinate and pipe axialdirection coordinate; a step for obtaining, in the event that themaximum luminance is less than the predetermined fixed threshold value,each of maximum luminance in the pipe axial direction at a givenwidth-direction coordinate on the optical cutting image, and maximumluminance in background texture region outside of the irradiation rangeof the slit light; a step for performing interior division of themaximum luminance of the pipe axial direction and the maximum luminanceof the background texture region by a ratio determined beforehand, andsetting the obtained luminance as a threshold value; a step for taking aluminance greater than the threshold value and a weighted mean of pipeaxial direction coordinates indicating the luminance aspseudo-cross-sectional direction coordinates for the width-directioncoordinates and pipe axial direction coordinates; and a step forcalculating the bead cutting shape of the electric resistance weldedpipe based on a pseudo-cross-sectional shape obtained by stringingpseudo-cross-sectional direction coordinates in the width direction, anda predetermined conversion expression determined from a geometricpositional relation of the light source of the slit light, theimage-taking means, and the electric resistance welded pipe.

According to a third aspect of the present invention, a measurementdevice for a bead cutting shape of an electric resistance welded pipe,comprises: a slit light source for irradiating slit light at a givenincident angle on a bead portion of an electric resistance welded pipefollowing cutting; image-taking means for taking an irradiation image ofthe slit light at a different receiving angle; a first computationcircuit for calculating, with regard to the optical cutting image outputfrom the image-taking means, the maximum luminance in the pipe axialdirection at a given width-direction coordinate on the optical cuttingimage, and the pipe axial direction coordinate where the maximumluminance occurs; a second computation circuit for calculating themaximum luminance in background texture region, at a position removed bya predetermined number of pixels or more from a pipe axial directioncoordinate where the maximum luminance in the pipe axial directionoccurs at a given width-direction coordinate; an accumulation circuitfor calculating a luminance which is greater than a threshold calculatedfollowing a predetermined computation expression from the firstcomputation circuit and the second output computation circuit, and theweighted mean of pipe axial direction coordinates indicating theluminance; an image reconfiguring circuit for stringing the weightedmean of pipe axial direction coordinates thus calculated to generate apseudo-cross-sectional shape in the width direction; and a coordinatescomputation circuit for calculating and displaying the bead cuttingshape of the electric resistance welded pipe based on a predeterminedconversion expression determined from a geometric positional relation ofthe slit light source, the image-taking means, and the electricresistance welded pipe.

According to a fourth aspect of the present invention, a measurementdevice for a bead cutting shape of an electric resistance welded pipe,the device comprising: a slit light source for irradiating slit light ata given incident angle on a bead portion of an electric resistancewelded pipe following cutting; image-taking means for taking anirradiation image of the slit light at a different receiving angle; afirst computation circuit for calculating, with regard to the opticalcutting image output from the image-taking means, the maximum luminancein the pipe axial direction at a given width-direction coordinate on theoptical cutting image, and the pipe axial direction coordinate where themaximum luminance occurs; a branch circuit for judging whether or notthe maximum luminance in the pipe axial direction at the certain widthdirection is equal to or greater than a predetermined fixed thresholdvalue; a second computation circuit for calculating the maximumluminance in background texture region, at a position removed by apredetermined number of pixels or more from a pipe axial directioncoordinate where the maximum luminance in the pipe axial directionoccurs at a given width-direction coordinate; a first accumulationcircuit for calculating the weighted mean of pipe axial directioncoordinates greater than a threshold obtained by interior division ofthe maximum luminance in the pipe axial direction at the certain widthdirection, and the maximum luminance at background texture region, by apredetermined ratio; a second accumulation circuit for calculating theluminance equal to or greater than the predetermined fixed thresholdvalue and the weighted mean of pipe axial direction coordinatesindicating the luminance; an image reconfiguring circuit for selectingthe output of the first accumulation circuit and the second accumulationcircuit thus calculated following output from the branch circuit andstringing the output in the width direction so as to generate apseudo-cross-sectional shape; and a coordinates computation circuit forcalculating and displaying the bead cutting shape of the electricresistance welded pipe based on a predetermined conversion expressiondetermined from a geometric positional relation of the slit lightsource, the image-taking means, and the electric resistance welded pipe.

According to a fifth aspect of the present invention, with a measurementmethod for a bead cutting shape of an electric resistance welded pipe,for calculating the bead shape of an electric resistance welded pipe bysubjecting to predetermined image processing an optical cutting imageobtained by taking an image of slit light irradiated on a bead generatedon the inner face or outer face of an electric resistance welded pipe ata welding portion with image-taking means from an angle different to theirradiation direction of the slit light, an image obtained by overlayingthe optical cutting image and an optical cutting image followingthinning processing of the optical cutting image by predeterminedprocessing means is displayed.

The color of each pixel in the optical cutting image following thinningmay be colored with a color corresponding to an SN ratio determined by aratio between the luminance of the optical cutting image on an opticalcutting image corresponding to the pixel, and the maximum luminance in aregion outside of the slit light, and be displayed.

The color of each pixel in the optical cutting image following thinningby predetermined image processing means of an optical cutting imageobtained by taking an image of irradiated slit light with image-takingmeans from an angle different to the irradiation direction of the slitlight, may be categorized and colored with a color corresponding to anSN ratio determined by a ratio between the luminance of the opticalcutting image on the optical cutting image corresponding to the pixel,and the maximum luminance in a region outside of the slit light, and beoverlaid with the optical cutting image and displayed.

According to a sixth aspect of the present invention, a measurementdevice for a bead cutting shape of an electric resistance welded pipecomprises: a slit light source for irradiating slit light at a givenincident angle on a bead portion of an electric resistance welded pipefollowing cutting; image-taking means for taking an irradiation image ofthe slit light at a different receiving angle; a thinning processingcircuit for processing the optical cutting image output from theimage-taking means so as to display the image of the slit light with onepixel; and an image synthesizing circuit for overlaying the opticalcutting image, and the results of the thinning, on the same image.

According to a seventh aspect of the present invention, a measurementdevice for a bead cutting shape of an electric resistance welded pipecomprises: a slit light source for irradiating slit light at a givenincident angle on a bead portion of an electric resistance welded pipefollowing cutting; image-taking means for taking an irradiation image ofthe slit light at a different receiving angle; a thinning processingcircuit for processing the optical cutting image output from theimage-taking means so as to display the image of the slit light with onepixel; and a thinning circuit for coloring the color of each pixel inthe thinned optical cutting line corresponding to an SN ratio determinedby a ratio between the luminance of the slit light image on the opticalcutting image corresponding to the pixel, and the maximum luminance in aregion outside of the slit light.

The measurement device may further comprise an image synthesizingcircuit for overlaying the optical cutting image and the colored resultsof the thinning output by the thinning circuit on the same image.

According to an eighth aspect of the present invention, an electricresistance welded pipe bead shape detecting method, for detecting thebead shape of an electric resistance welded pipe by the optical cuttingmethod, wherein an image, obtained by a slit light being irradiated or apoint light being scanned on a welding portion of an electric resistancewelded pipe and an image of the slit light irradiated on the surface ofthe welding portion or an image of the track of the point light scannedthereupon being taken with image-taking means from an angle different tothe irradiation direction of the slit light, is subjected topredetermined image processing, comprises: a step for calculatingcoordinates for a temporary bead apex by a predetermined calculationexpression from a profile of an electric resistance welded pipe; a stepfor obtaining a first approximation curve by approximating the profileof the electric resistance welded pipe with a quadratic function; a stepfor calculating the coordinates for two intersecting points on eitherside of the temporary bead apex from the profile of the electricresistance welded pipe and the first approximation curve; a step forcalculating a temporary existence range of the bead by a predeterminedcalculation expression from the coordinates of the temporary bead apex,and the coordinates of two intersection points on either side of thetemporary bead apex; a step for obtaining a second approximation curveby approximating a base pipe shape excluding the temporary existencerange of the bead from the profile of the electric resistance weldedpipe with an polynomial expression of a degree which is even andquadratic or higher; and a step for determining, of regions wherein thedeviation between the profile of the electric resistance welded pipe andthe second approximation curve is greater than a predetermined thresholdvalue, a region containing the coordinates of the temporary bead apex asbeing the bead.

According to a ninth aspect of the present invention, an electricresistance welded pipe bead shape detecting device comprises: lightprojecting means for irradiating a slit light or scanning a point lighton a welding portion of an electric resistance welded pipe at a givenangle; image-taking means for taking an image of the projected lightirradiated on the welding portion by the light projecting means, from anangle different to the given angle; profile calculating means forcalculating a profile of the electric resistance welded pipe bysubjecting the image obtained from the image-taking means topredetermined image processing; temporary bead apex detecting means forcalculating coordinates for a temporary bead apex by a predeterminedcalculation expression from the profile of the electric resistancewelded pipe; first regression computation means for approximating with apredetermined regression expression, with the profile of the electricresistance welded pipe as a quadratic function; intersecting pointcalculating means for calculating the coordinates for two intersectingpoints on either side of the temporary bead apex from the output of thefirst regression computation means and the output of the profilecalculating means; first range calculating means for calculating atemporary existence range of the bead by a predetermined calculationexpression from the coordinates of the intersection points and thecoordinates of the temporary bead apex; second regression computationmeans for approximating the profile of the electric resistance weldedpipe excluding the temporary existence range of the bead thuscalculated, with an polynomial expression of a degree which is even andquadratic or higher; and second range calculating means for outputting,of regions wherein the deviation between output from the secondegression computation means is greater than a predetermined thresholdvalue and the profile of the electric resistance welded pipe, a regioncontaining the coordinates of the temporary bead apex as being the beadrange.

According to a tenth aspect of the present invention, an electricresistance welded pipe bead shape detecting method, for detecting thebead shape of an electric resistance welded pipe, wherein an image,obtained by a slit light being irradiated or a point light being scannedon a pipe surface including a bead portion due to welding of an electricresistance welded pipe, and an image of the slit light irradiated on thepipe surface including the bead portion or an image of the track of thepoint light scanned thereupon being taken with image-taking means froman angle different to the irradiation direction of slit light, issubjected to predetermined image processing, comprises: a step forobtaining shape data of a portion of the pipe surface equivalent to thebead portion from shape data of the pipe surface including the beadportion calculated in the image processing, from preset boundaries atthe left and right edges of the bead portion, and an apex position ofthe bead portion calculated separately; a step for dividing the shapedata of the portion of the pipe surface equivalent to the bead portioninto two regions, left and right; a step for performing approximationwith a function with regard to each of the left and right shape data, soas to obtain approximation functions for the left and right bead shapes;a step for performing further approximation with a function, with regardto base pipe shape data excluding the pipe surface shape data of theportion equivalent to the bead portion from the shape data of the pipesurface including the bead portion, so as to obtain base pipe shapeapproximation functions; and a step for calculating at least one of thewidth, height, slope angle, and step at the left and right boundariesbetween the bead portion and base pipe, based on each of the left andright bead shape approximation functions, and the base pipe shapeapproximation function.

Calculations may be performed to minimize the error between the left andright bead shape approximation functions and the shape data of the pipesurface including the bead portion, with approximation functions for theleft and right bead shapes as functions wherein two or more straightlines with different inclinations are linked, and with the position ofthe linking points, the inclination of the straight lines, andintercept, as parameters.

The intersecting points between the left and right bead shapeapproximation functions and the base pipe shape approximation functionmay be calculated as the boundaries of both edges of the bead portion;with at least one of the bead width, height, slope angle, and step atthe left and right boundaries between the bead portion and base pipe,being calculated, based thereupon.

The deviation in the bead shape approximation function values and thebase pipe shape approximation function values at the electric resistancewelded pipe cross-sectional direction position on the apex of the beadportion may be calculated as the bead height.

The intersecting points between the left and right bead shapeapproximation functions and the base pipe shape approximation functionmay be calculated as the boundaries of both edges of the bead portion,with respective differential coefficients being calculated for theintersecting points between the left and right bead shape approximationfunctions and the base pipe shape approximation function at the electricresistance welded pipe cross-sectional direction position, and the leftand right bead slope angles being each calculated, based thereupon.

According to an eleventh aspect of the present invention, an electricresistance welded pipe bead shape detecting device comprises: lightprojecting means for irradiating a slit light or scanning a point lighton a pipe surface including a welding portion of an electric resistancewelded pipe; image-taking means for taking an image of the projectedlight irradiated on the pipe surface including the welding portion, froman angle different to that of the light projecting means; bead shapecalculating means for calculating the bead shape of the electricresistance welded pipe by subjecting the image obtained from theimage-taking means to predetermined image processing; an apex positionsetting circuit and a bead range setting circuit, for calculating thebead apex position and each of the boundary positions between the beadportion and the base pipe excluding the bead portion, based on the beadshape data calculated by the bead shape calculating means; a bead shapeapproximation circuit for calculating approximation functions for theleft and right bead shapes, based on the apex position output from theapex position setting circuit and bead range setting circuit and theleft and right boundary positions on either side of the bead apexposition; a base pipe shape approximation circuit for calculating a basepipe shape approximation function, based on base pipe shape data furtheroutwards from the left and right boundary positions which the bead rangesetting circuit outputs; a bead range re-setting circuit for re-settingthe intersections between the left and right bead shape approximationfunctions output by the bead shape approximation circuit, and the basepipe shape approximation function output from the base pipe shapeapproximation circuit as left and right boundary positions; and afeatures calculating circuit for calculating at least one of the beadwidth, height, slope angle, and step at the left and right boundariesbetween the bead portion and base pipe, based on the output of each ofthe bead range setting circuit, bead shape approximation circuit, andbase pipe shape approximation circuit.

According to the present invention, the bead cutting shape of electricresistance welded pipe can be precisely measured without being affectedby the difference in luminance level between the cut portion and uncutportion in optical cutting images. The features of the electricresistance welded pipe bead shape are calculated based on the shape dataof the pipe surface, so the bead shape can be detected without beingaffected by changes in the magnetic permeability of the welded portions.The bead shape can be accurately detected even in cases wherein the beadslopes are extremely smooth or the bead height is low, in cases whereinthe height of the bead is irregular in the longitudinal direction, or incases wherein the bead shape is not a triangle or trapezoid, or in caseswherein the bead shape is steep. Also, the bead cutting shape data canbe automatically computed and recorded, so not only is the opticalcutting image visually monitored; rather, combining this withquantitative judgement and understanding inclinations, and furthercutting position control, enables advanced electric resistance weldedpipe manufacturing operations to be carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1C are diagrams illustrating the operations of thepresent invention;

FIG. 2 is a flowchart illustrating a calculating method for an opticalcutting line according to a first explanatory arrangement of the presentinvention;

FIG. 3 is a flowchart illustrating a calculating method for an opticalcutting line according to a second explanatory arrangement of thepresent invention;

FIG. 4 is a schematic diagram illustrating an inner face bead trimmercomprising a bead cutting shape measurement device for an electricresistance welded pipe according to the present invention;

FIG. 5 is a block diagram illustrating the configuration of principalcomponents of the bead cutting shape measurement device according to thepresent invention;

FIG. 6 is a diagram illustrating an optical cutting image measurementexample of a bead cutting portion of an electric resistance welded pipeaccording to a first embodiment of the present invention;

FIG. 7 is a diagram illustrating the bead cutting shape of the electricresistance welded pipe output by an image reconfiguring circuit of thefirst embodiment with regard to the measured image shown in FIG. 6;

FIG. 8 is a diagram illustrating an example wherein a shape abnormalityhas been observed in the output of the first embodiment at the time ofmanufacturing a different electric resistance welded pipe;

FIG. 9 is a diagram illustrating the results of collecting a sample ofthe bead cutting portion on the inner side of the pipe equivalent toFIG. 8, and performing off-the-line measurements of the bead cuttingshape;

FIG. 10 is a block diagram illustrating the configuration of principalcomponents of the bead cutting shape measurement device according to asecond embodiment of the present invention;

FIG. 11 is a diagram illustrating optical cutting image measurementresults of the bead cutting portion of the electric resistance weldedpipe according to the same;

FIG. 12 is a diagram illustrating the bead cutting shape of the electricresistance welded pipe output by an image reconfiguring circuit of thesecond embodiment with regard to the measured image shown in FIG. 11;

FIG. 13 is a schematic diagram illustrating the principle of opticalcutting method;

FIG. 14 is a diagram illustrating an example wherein a portion of theluminance of the optical cutting image has markedly deteriorated, in theevent of measuring the bead cutting portion of the electric resistancewelded pipe with the optical cutting method;

FIG. 15 is a schematic diagram illustrating an inner face bead trimmercomprising a bead cutting shape measurement device for an electricresistance welded pipe according to the present invention;

FIG. 16 is a block diagram illustrating the configuration of principalcomponents of the bead cutting shape measurement device according to thepresent invention;

FIG. 17 is a diagram illustrating an optical cutting image measurementexample of a bead cutting portion of an electric resistance welded pipeaccording to the first embodiment of the present invention;

FIG. 18 is a diagram illustrating an example of an image wherein theoptical cutting image at the bead cutting portion of the electricresistance welded pipe has been subjected to thinning processing;

FIG. 19 is a diagram illustrating an example of an image output by animage synthesizing circuit;

FIG. 20 is a block diagram illustrating the configuration of principalcomponents of the bead cutting shape measurement device according to thesecond embodiment of the present invention;

FIG. 21 is a diagram illustrating an optical cutting image measurementexample of the bead cutting portion of the electric resistance weldedpipe;

FIG. 22 is a diagram illustrating an example of an image wherein theoptical cutting image at the bead cutting portion of the electricresistance welded pipe has been subjected to thinning processing;

FIG. 23 is a diagram illustrating an example of an image output from thethinning circuit;

FIG. 24 is a block diagram illustrating the configuration of principalcomponents of the bead cutting shape measurement device according to athird embodiment of the present invention;

FIG. 25 is a diagram illustrating an optical cutting image measurementexample of the bead cutting portion of the electric resistance weldedpipe;

FIG. 26 is a diagram illustrating an example of an image wherein theoptical cutting image at the bead cutting portion of the electricresistance welded pipe has been subjected to thinning processing;

FIG. 27 is a diagram illustrating an example of an image output by theimage synthesizing circuit according to the same;

FIG. 28 is a schematic diagram illustrating the principle of opticalcutting method;

FIG. 29 is a diagram illustrating an example wherein a portion of theluminance of the optical cutting image has markedly deteriorated in theevent of measuring the bead cutting portion of the electric resistancewelded pipe with the optical cutting method;

FIG. 30 is a diagram illustrating an example wherein a halation isobserved at the uncut portion in the event of raising the luminance ofthe cut portion;

FIG. 31 is a schematic diagram illustrating the configuration ofprincipal components of the welding bead detecting device for theelectric resistance welded pipe according to the present invention;

FIG. 32 is a block diagram illustrating the configuration of acomputation circuit group making of a profile data processing device;

FIG. 33 is a diagram illustrating an example of an optical cutting imagenear the bead of a electric resistance welded pipe;

FIG. 34 is a diagram illustrating profile data wherein the opticalcutting image near the bead of a electric resistance welded pipe hasbeen subjected to thinning processing;

FIG. 35 is a diagram illustrating the state of a first approximationcurve of a quadratic function calculated with regression computationperformed on the entire profile data, which the first regressioncomputation circuit outputs;

FIG. 36 is a diagram illustrating the state of a second approximationcurve of a quartic function obtained as the result of least-squareregression computation performed on the range of the first rangecalculating circuit, output by a second regression computation circuit;

FIG. 37 is a plotted diagram of deviation e(x) between the quarticfunction and the profile data, calculated by a deviation calculationcircuit;

FIG. 38 is a diagram comparing this embodiment with a photograph of anactual welding bead taken in the same optical system displacement;

FIG. 39 is a diagram illustrating the relation between the degree of apolynomial and the RMS (root-mean-square) of approximation error, in acase of regression of the upper half curve portion of the ellipse withquadratic, quartic, sextic, and octic polynomials;

FIG. 40 is a schematic diagram illustrating the configuration ofprincipal components of a bead shape detecting device of the electricresistance welded pipe according to the present invention;

FIG. 41 is a block diagram illustrating the configuration of a circuitgroup making up the bead shape calculating means;

FIG. 42 is a diagram illustrating an example of an optical cutting imageon the surface of the electric resistance welded pipe including the beadportion;

FIG. 43 is a diagram illustrating shape data for the surface of theelectric resistance welded pipe including the bead portion, with anoptical cutting image subjected to thinning processing, according to thepresent invention;

FIG. 44 is a diagram plotting the relation between each x_(p) and theapproximation error E(x_(p)), with regard to, of the shape data of thepipe surface including the bead portion shown in FIG. 43, the shape datato the left side of the apex position;

FIG. 45 is a diagram illustrating the relation between the degree of apolynomial and the RMS (root-mean-square) of approximation error, in acase of regression of the upper half portion of a circle with quadratic,quartic, sextic, and octic polynomials; and

FIG. 46 is a diagram with regard to an embodiment of the bead shapedetection method according to the present invention, wherein left andright bead shape approximation functions f_(L)(x) and f_(R)(x)calculated by the bead shape approximation circuit, and the base pipeshape approximation function f_(p)(x) calculated by the base pipe shapeapproximation circuit, are plotted along with shape data of the pipesurface including the bead portion;

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of embodiments of the presentinvention, with reference to the drawings.

First, two explanatory arrangements will be given as examples ofembodiments of the present invention, for the purpose of explaining theprinciple of the present invention, following which the First Embodimentand subsequent embodiments will be described.

In a case of taking an optical cutting image with two-dimensionalimage-taking means such as a CCD camera, a region having both backgroundtexture and a slit light irradiation region can be expected to bedisplayed on a display screen. This will hereafter be referred to as an“optical cutting image”. In an optical cutting image, the opticalcutting image of the slit light irradiation region is captured as atwo-dimensional mesh display image such as shown in FIG. 1A. In FIG. 1A,with the corner further to the bottom left of a bottom left corner pixelsectioned by the two-dimensional mesh as the origin, and with the X axisin the width direction and the Y axis in the pipe axial direction, adiagonal line center can be taken for a representative point for thepixel at the lower left corner, with the coordinates thereof as X=X1,and Y=Y1. Accordingly, each pixel can be determined by coordinates X=Xi,Y=Yj.

Let us say that the aforementioned optical cutting image displays anoptical cutting image of the slit light irradiation region including thebackground texture, and for a given pixel represented by the Xcoordinate X=Xi and the Y coordinate Y=Yj in the optical cutting image,the luminance at that pixel is I(Xi, Yj).

Let us further take the weighted mean S(Xi) of the Y coordinate Yj andluminance I(Xi, Yj) as defined in the following expression as the Ycoordinates on the optical cutting line at X=Xi.S(Xi)=ΣYj I(Xi, Yj)/ΣI(Xi, Yj)

Now, in the event that there is a disturbance component such as indirectreflection light or background light in the portion outside of theirradiation region of the slit light, such as the background textureportion shown in FIG. 1B, this component will also be added, resultingin error, but the maximum luminance in the Y-axial direction in theoptical cutting image is the slit light irradiation region, with littleexpansion in the Y-axial direction, the extent of which can be describedbeforehand. The range of Y coordinates in the portion outside of theslit light irradiation region can be taken as noise.

Accordingly, the Y coordinates of the optical cutting line at each Xcoordinate is obtained by the following procedures (1) through (3).

(1) The Y coordinate Y0 where the Y-axial direction luminance is thegreatest (in the event that multiple coordinates exist, the averagethereof), and the luminance I0 at that point, are obtained.

(2) The maximum luminance I1 in the range of0≦Y≦Y0−N _(w) ΔY, Y0+N _(w) ΔY≦Y≦Yn

wherein Yn is a representative Y coordinate of a pixel at theY-directional edge of the optical cutting image, and ΔY represents theY-directional length of one pixel, is obtained, using a predeterminednumber of pixels, denoted by N_(w).

(3) An appropriate value between I0 and I1 (e.g., an average value(I0+I1)/2) is set as a threshold value J1, and S(Xi) is calculated inthe range of Y wherein the pixel luminance in the Y direction is greaterthan J1.

(4) The above procedures (1) through (3) are repeated with the relativemovement of the slit light irradiation region in the pipe axialdirection.

The procedures for the Y coordinate calculation method for the opticalcutting line according to this first explanatory arrangement are shownas a flowchart in FIG. 2, and such computation allows the opticalcutting image of the bead cutting shape of the electric resistancewelded pipe to be precisely measured without being affected bydifference in the luminance level at the cut portion and uncut portionof the optical cutting image.

Also, in the event that the intensity of the reflected light at theuncut portion further causes halation such as indicated by thewhited-out portion in FIG. 1A, that is to say, in the event that theintensity of the reflected light at the uncut portion is high enough toexceed the luminance measurement range as shown in FIG. 1C, or, in theevent that the noise from the background texture portion is low enoughto be negligible, cross-section line calculation of regions with suchhigh reflection light intensity may be substituted with a predeterminedfixed threshold value J2. That is to say, the following procedures maybe followed instead of the above-described procedures.

(1) The Y coordinate Y0 where the Y-axial direction luminance is thegreatest (in the event that multiple coordinates exist, the averagethereof), and the luminance I0 at that point, are obtained.

(2) The maximum luminance I1 in the range of0≦Y≦Y0−N _(w) ΔY, Y0+N _(w) ΔY≦Y≦Yn

wherein Yn is a representative Y coordinate of a pixel at theY-directional edge, and ΔY represents the Y-directional length of onepixel, is obtained, using a predetermined number of pixels, denoted byN_(w).

(3) In the event that I0 is equal to or exceeds the fixed thresholdvalue J2, S(Xi) is calculated in the range of Y wherein the pixelluminance in the Y direction at X=Xi is equal to or greater than J2.

In this case, J2 may be set to be the maximum value of the luminancerange, or may be set somewhat lower than the maximum value of theluminance range, in the range shown by experience not to be equal to orlower than the maximum luminance of the background texture portion.

(4) In the event that I0 is less than the fixed threshold value J2, anappropriate value between I0 and I1 (e.g., an average value (I0+I1)/2)is set as a threshold value J3 (equivalent to J1 in the firstexplanatory arrangement), and S(Xi) is calculated in the range whereinthe pixel luminance in the Y direction is greater than J3.

(5) The above procedures (1) through (4) are repeated with the relativemovement of the slit light irradiation region in the pipe axialdirection.

The procedures for the Y position calculation method for the opticalcutting line according this second explanatory arrangement are shown asa flowchart in FIG. 3, and such computation allows the optical cuttingimage of the bead cutting shape of the electric resistance welded pipeto be precisely measured without being affected by difference in theluminance level at the cut portion and uncut portion of the opticalcutting image.

The slit light irradiation image, which is a pseudo-cross-sectionalshape image so as to say, on the electric resistance welded pipe is thuscalculated using the optical cutting method. Now, the X coordinate and Ycoordinate of the optical cutting line representing the slit lightirradiation image with a weighted mean in the skit width direction arethe pixel address of the optical cutting image, and in the example ofthe two explanatory arrangements described above, this is a set of twovalues with the lower left corner of the optical cutting image as theorigin (0, 0), which can be readily converted into a full-scale truecross-sectional shape of the electric resistance welded pipe beadcutting shape.

That is to say, defining the direction perpendicular to both the pipeaxis and the width direction as having a 0° directional angle, with theincident angle of the light source as α and the receiving angle of theimage-taking means as β, and further with slit light for the lightsource and with a camera serving as the image-taking means, in a casewherein a plane formed by the optical axis of the slit light and theoptical axis of the camera is disposed perpendicular to the tangentialplane of the electric resistance welded pipe at the image-takingposition, the cross-sectional position (xi, yj) on the image can beconverted by geometric formula into coordinates (xi, yj) for thefull-scale true cross-sectional shape of the electric resistance weldedpipe bead cutting shape by the expressionsxi=Xiyj=ΔY×Yj×cos α/sin(α+β)

wherein ΔY represents the length of one pixel in the y direction.

Or, an arrangement may be used wherein a sample wherein dimensions arealready known is taken, and conversion coefficients are adjusted from(Xi, Yj) to (xi, yj), instead of the above expression.

In electric resistance welded pipe manufacturing, the width of thewelding beard before cutting is around 1/10 to ⅕ of the outer diameterof the pipe, and the position where the welding bead is can be generallyknown beforehand. The reason is that with general electric resistancewelded pipe manufacturing lines, the metal strip which is the materialuninterruptedly continues from uncoiling of the metal strip coil of basematerial, through the formation and welding stages of the pipe, and theposition and direction thereof is restricted by the formation rolls andso forth, so even in the event that horizontal movement of the pipe(change in path line), twisting, etc., does occur, the maximum extentthereof is around the width of the bead or so. Here, the bead portionmay be anywhere on the circumference of the pipe, but the followingdescriptions will be made with the bead portion at around the top of thepipe, to facilitate description. Of course, this assumption does notdiminish the generality thereof in any way.

Now, detecting the pipe shape including the bead portion over a rangesufficiently wider than the bead width (hereafter referred to as“profile of electric resistance welded pipe”) with an appropriate methodand approximating the detected profile of the electric resistance weldedpipe with a quadratic function, the approximation curve attempts toapproximate not only the base pipe portion but also the protruding shapeof the bead portion thereupon at the same time, so the curve is a curvewhich passes above the profile of the base pipe portion and below theapex of the bead portion. This curve is a first approximation curve.Now, the general apex position Xc of the bead portion can be obtainedwith separate means, and points X1 and Xr where the first approximationcurve and the profile of the electric resistance welded pipe intersectcan be obtained by searching to the left and right from the general apexposition, thereby obtaining a general bead range R (X1′ to Xr′) from thecoordinates of X1, Xr, and Xc.

Now, the first approximation curve is restricted to a quadraticfunction. The reason is that, while the shape of the pipe is essentiallyhorizontally symmetrical with regard to the apex of the bead portion, soapproximation with an even function such as a polynomial of an evendegree should suffice, approximation with a quartic polynomial or highershowed that inflection points are generated on the approximation curvewhich accentuate the bead portion, causing adverse effects with regardto calculation of the intersecting points with the base pipe portion.Accordingly, using only a quadratic function avoids this problem.

Next, performing approximation of the profile of the range excluding Rat the width-direction coordinate (X coordinate) with a polynomial of aneven degree, quadratic or higher, the shape of the base pipe portion canbe approximately quite precisely. This is a second approximation curve.

The basis for this is shown in the graph in FIG. 39, which indicates therelation between the degree of the polynomial and the RMS(root-mean-square) of the approximation error in the event that thecurve at the upper half of an ellipse is subjected to regression withquadratic, quartic, sextic, and octic polynomials. This indicates thatregression of the shape of the ellipse can be made with sufficientprecision by a polynomial of an even degree, quadratic or higher, andpreferably with a polynomial of an even degree, quartic or higher.

This nature can be used to compare the profile of the base pipe portionapproximately with sufficient precision with the profile of the electricresistance welded pipe including the bead portion, so as to determinethe region containing the coordinates of the bead apex in the rangewherein the deviation of the profiles is greater than a predeterminedthreshold to be the bead.

The above computation uses a polynomial as the approximation curve, sousing the least-square method allows regression computation to beperformed simply with addition, multiplication, and matrix computation.That is to say, none of the assumptions of circularity and differentialcomputations and the like which have been problematic with theconventional art are used, so there are no effects of noise, and also,complicated procedures such as moving averages for noise removal ornoise data removal operations per coordinate are unnecessary.

Embodiments

The following is a description of embodiments of the present invention,with reference to the drawings.

First Embodiment

FIG. 4 illustrates around a bead trimmer 112 on the inner face of theelectric resistance welded pipe 110, with reference numeral 114 denotinga cutting tool, 116 denoting a supporting arm, 150 denoting ameasurement head of a bead cutting shape measurement device according tothe present invention, 170 denoting a control device, 190 denoting adisplay device, and 192 denoting a recording device.

The measurement head 150 is placed downstream in the pipe transportationdirection of the cutting tool 114, preferably at a position 500 to 2000mm therefrom, preferably has a mechanism for protecting the measurementequipment from radiant heat and welding sparks from the welding seam,and scattering of cooling water, and preferably has a gas purgingmechanism handling both cleansing and cooling, in order to preventoverheating of the optical system and soiling thereof by water, oil,fumes, and so forth.

Also, the control device 170, display device 190, and recording device192 are preferably positioned at a working position away form themanufacturing line, for example, near an operating board not shown inthe drawings to be operated by an operator, and connected to themeasurement head 150 by a cable 160 through a supporting arm 116 or thelike, with a shielded configuration to prevent intrusion of electricnoise or the like along the way.

Now, while the description of the following embodiment will be maderegarding a configuration for measuring the bead cutting shape on theinner side of the pipe, it is needless to say that the measurementmethod and device for the electric resistance welded pipe bead cuttingshape according to the present invention may be equally applied to theouter face or the inner face of the pipe.

Next, the configuration of the measurement head 150 and the controldevice 170 will be described with reference to FIG. 5. In FIG. 5,reference numeral 120 denotes a slit light source, 130 denotes a CCDcamera, 132 denotes a lens, 124 denotes light source power source, 134denotes camera power source, and 172 denotes an image data conversioncircuit.

Here, the light source power source 124, camera power source 134, imagedata conversion circuit 172, and the later-described computation circuitgroup are preferably stored in one case as a control device 170. Thecomputation circuit group is a first computation circuit 174, a secondcomputation circuit 176, a integration circuit 178, an imagereconfiguring circuit 180, and a coordinates computation circuit 182.

The slit light source 120 is within the measurement head 150 andirradiates a slit light 121 which has an angle α as to the cross-sectionof the electric resistance welded pipe 110, has a predeterminedirradiation width in the pipe circumferential direction (widthdirection), and forms the irradiation weight of a rectangular irradiatedimage as narrow as possible in the pipe axial direction, preferably 0.05mm or less, and in this aspect, the present embodiment has the samearrangement as with conventional art.

Now, arrangements using a semiconductor laser device of thelight-emitting unit are widely used for the slit light, and arrangementsusing a combination of knife-edge screens and cylindrical lenses or thelike to make the irradiated image rectangular are commerciallyavailable.

Also, the closer this angle α is to 90°, the more the bead cutting shapeobserved with the later-described camera 130 is expanded in the pipeaxial direction, but at the same time increases the effects of distancefluctuations between the measurement head 150 and the inner face of thepipe, so the present embodiment uses α=70° as a suitable value takingthe balance of both into consideration, based on prior experiments.

The camera 130 observes the irradiation image of the slit lightirradiated onto the bead cutting portion from an angle β as to thecross-section of the electric resistance welded pipe 110, and ITVs orcameras using semiconductor devices such as CCD or CMOS which are widelyused in industrial fields can be used. Also, a commercially-availablecamera lens may be used for the lens 132 for image formation by thecamera, but a band-pass filter having a passage wavelength band matchingthe wavelength of the light source in order to eliminate unnecessarylight such as background light or the like from the optical cuttingimage, and a heat-ray cut filter or the like for preventing damage tothe image-taking surface of the camera and the lens from radiant heat,should be provided as necessary.

The measurement head 150 is preferably a sealed structure for protectingthe optical equipment such as the camera 130, light source 120, lens132, etc., within from heat and water and the like, and in this case, apreferably configuration has windows 152 and 154 for only the slit lightand camera field of view portions, respectively.

The position angle of the camera 130 is preferably such that (α+β) isgenerally 90°, with the number of pixels of the camera and the field ofview being determined based on the width of the bead portion and thenecessary resolution. With the present invention, the slit lightirradiation angle from the light source 120 is α=70°, the image-takingangle is β=30°, the range of the field of view is 25 mm wide and 20 mmhigh, and the number of pixels is 1300 horizontally by 1000 vertically,as a suitable value. Thus, the height-wise resolution is20/1000*cos(70°)/sin(70°+30°)=0.0069 mm. Also, the width-wise resolutionis 25/1300=0.0192 mm, so the bead cutting state can be monitored with aresolution of 20 μm in the width direction (circumferential direction)and 7 μm in the height direction (pipe axial direction).

Also, it is needless to say that the light source 120 and camera 130should be positioned such that the optical axes thereof intersectprecisely over the bead cutting portion, and further, the plane formedby the axial axes of the light source 120 and camera 130 even morepreferably contains the direction of progression of the electricresistance welded pipe 110, i.e., the center axis of the pipe. Thereason is that this arrangement of the light source and the cameraallows the optical cutting image on the inner face of the pipe to behorizontally symmetrically taken with regard to a virtual center lineextending in the Y-axial direction on the optical cutting image.

Further, the light source 120 and the camera 130 may be fixed to themeasurement head 150 in an inclined state as shown in FIG. 5, or may bedisposed so that their optical axes are both parallel to the centralaxis within the electric resistance welded pipe to reduce the size ofthe device, with the angle of the optical axis being changed by thereflection mirror 136.

Next, the configuration of the components of the control device 170 willbe described. The image data conversion circuit 172 converts each pixelof image signals output form the camera 130 into luminance data andoutputs, and an image board (frame-grabber) widely commerciallyavailable in recent years, which is compatible with the camera 130, canbe used.

The first computation circuit 174 is for calculating the maximumluminance I0 in the Y-axial direction and the Y coordinate Y0 showingthe maximum luminance, for each X coordinate Xi (i=0 through N) in theacquired image, and the second computation circuit 176 is forcalculating the maximum luminance I1 of the background texture in thepixel data in the Y-axial direction (0≦Y≦Y0−N_(w)ΔY, Y0+N_(w)ΔY≦Y≦Yn),using Y0 and the number of offset pixels set beforehand N_(w) and theY-directional length of one pixel ΔY. The second computation circuit 176may have the same configuration as the first computation circuit 174,except for the computation range being different.

The integration circuit 178 calculates a threshold value J1 by apredetermined internal division ratio from the I0 and I1 thuscalculated, and calculates the weighted mean S(Xi) only in the rangewherein, of one line pixel in the Y direction wherein X=Xi, the pixelluminance is greater than J1. With the present embodiment, the internaldivision ratio is 1:1, so this is calculated by J1=(I0+I1)/2.

The image reconfiguring circuit 180 reconfigures the weighted mean S(Xi)output for each X coordinate as described above into an image pictureQ(Xi, Yj) as optical cutting shapes at each X=Xi.

The coordinates computation circuit 182 converts a string of opticalcutting line coordinates (a set of an X coordinate and a Y coordinateindicating the position of the optical cutting line at each Xcoordinate) output by the image reconfiguring circuit 180 based on apredetermined conversion expression determined by the placement of theoptical system and the resolution of the camera, into the full-scaledata of a true cross-sectional shape, and can be realized with a circuitwhich performs computation of (xi, yj), described in the section onoperations, for example.

Next, the results of implementing the present embodiment will bedescribed.

An optical cutting image, observed with the camera 130 through the lens132 from the slit light 121 irradiated from the light source 120 of thisdevice onto the bead cutting portion 111 while manufacturing theelectric resistance welded pipe 110, was as shown in FIG. 6, with theslit light irradiation image being bright and heavy at the uncutportion, and the slit light irradiation image at the cut portion beingdifficult to visually recognize.

On the other hand, the image output from the image reconfiguring circuit180 is as shown in FIG. 7, and even though the contrast of the opticalcutting image was extremely low at the cut portion, the fact that thecut was normal, and the manner in which the cut portion and uncutportion differ in curvature, could be observed. Also, the output imageof the image reconfiguring circuit 180 while manufacturing a differentelectric resistance welded pipe 110 was as shown in FIG. 8, wherein itcould be configured that the bead cutting was incomplete, due to somesort of cutting abnormality. A sample was collected of the bead cuttingportion on the inner side of the pipe equivalent to FIG. 8, andoff-the-line measurements were performed using a non-contact distancemeter, which showed that the height of the step at the incompletely cutportion was 0.15 mm as shown in FIG. 9, thereby confirming that the beadcutting shape is being measured accurately even in cases wherein thereare abnormalities in the cutting.

Second Embodiment

FIG. 10 is a block diagram illustrating the configuration of thecomputation circuit group within the measurement head according toanother embodiment of the present invention. The unshown bead trimmer112 and measurement head 150 to be mounted thereupon are of the sameconfiguration as those in the first embodiment, so description thereofwill be omitted.

Also, in FIG. 10, with regard to the first computation circuit 174,second computation circuit 176, integration circuit 178 (hereafterreferred to as “first integration circuit”), and image reconfiguringcircuit 180, the same articles as those used in the above firstembodiment may be employed here. Reference numeral 184 in the presentembodiment denotes a branch circuit and 186 denotes a second integrationcircuit.

The branch circuit 184 is a circuit for judging which of the maximumluminance I0 on the optical cutting line calculated by the firstcomputation circuit 174, and the fixed threshold value J2 setbeforehand, is greater, and causing one or the other of the firstintegration circuit 178 and the second integration circuit 186 tooperate. This can be configured with a commercially-available comparatorcircuit.

The first computation circuit 174 is for calculating the maximumluminance I0 in the Y-axial direction and the Y coordinate Y0 showingthe maximum luminance, for each X coordinate Xi (i=0 through N) in theacquired image, the branch circuit 184 is a circuit for judging whetheror not the maximum luminance I0 is greater than the predetermined fixedthreshold value J2, and the second integration circuit 186 calculatesthe weighted mean S(Xi) only in the range wherein, of one line pixel inthe Y direction wherein the pixel luminance is greater than thepredetermined fixed threshold value J2. With the present embodiment, thethreshold J1 of the integration circuit 178 in the above-described firstembodiment is replaced with the predetermined fixed threshold value J2.

The same image reconfiguring circuit 180 as that with theabove-described first embodiment may be used, with the branch circuit184 selecting either the first integration circuit 178 or the secondintegration circuit 184 as the input thereof.

Next, the results of implementing the present embodiment will bedescribed.

An optical cutting image of the bead portion on the inner face of theelectric resistance welded pipe observed with the present embodimentwhile manufacturing another electric resistance welded pipe 110, was asshown in FIG. 11, with the uncut portion to the right side exhibitinghalation so the optical cut line is markedly heavier than otherportions, and noise extending upwards and downwards, while the slitlight irradiation image at the cut portion is difficult to visuallyrecognize, as with the first embodiment. On the other hand, the imageoutput from the image reconfiguring circuit 180 is as shown in FIG. 12,and the bead cutting shape could be measured suitably without effects ofhalation or noise.

Third Embodiment

FIG. 15 illustrates around a bead trimmer 212 on the inner face of theelectric resistance welded pipe 210, with reference numeral 214 denotinga cutting tool, 216 denoting a supporting arm, 250 denoting ameasurement head of a bead cutting shape measurement device according tothe present invention, 270 denoting a control device, 290 denoting adisplay device, and 292 denoting a recording device.

The measurement head 250 is placed downstream in the pipe transportationdirection of the cutting tool 214, preferably at a position 500 to 2000mm therefrom, preferably has a mechanism for protecting the measurementequipment from radiant heat and welding sparks from the welding seam,and scattering of solution water, and preferably has a gas purgingmechanism handling both cleansing and cooling, in order to preventoverheating of the optical system and soiling thereof by water, oil,fumes, and so forth.

Also, the control device 270, display device 290, and recording device292 are preferably positioned at a working position away form themanufacturing line, for example, near an operating board not shown inthe drawings to be operated by an operator, and connected to themeasurement head 250 by a cable 260 through a supporting arm 216 or thelike, with a shielded configuration to prevent intrusion of electricnoise along the way.

Now, while the description of the following embodiment will be maderegarding a configuration for measuring the bead cutting shape on theinner side of the pipe, it is needless to say that the measurementmethod and device for the electric resistance welded pipe bead cuttingshape according to the present invention may be equally applied to theouter face or the inner face of the pipe.

Next, the configuration of the measurement head 250 will be describedwith reference to FIG. 16. In FIG. 16, reference numeral 220 denotes aslit light source, 230 denotes a camera, 232 denotes a lens, 224 denoteslight source power source, 225 denotes camera power source, and 272denotes an image data conversion circuit.

Here, the light source power source 224, camera power source 225, imagedata conversion circuit 272, and the later-described computation circuitgroup are preferably stored in one case as a control device 270. Thecomputation circuit group is a thinning processing circuit 275 and animage synthesizing circuit 281.

The slit light source 220 is within the measurement head 250 andirradiates a slit light 221 which has an angle α as to the cross-sectionof the electric resistance welded pipe 210, has a predeterminedirradiation width in the pipe circumferential direction (widthdirection), and forms the irradiation width of a rectangular irradiatedimage as narrow as possible in the pipe axial direction, preferably 0.05mm or less, and in this aspect, the present embodiment has the samearrangement as with conventional art.

Now, arrangements using a semiconductor laser device of thelight-emitting unit are widely used for the slit light, and arrangementsusing a combination of knife-edge screens and cylindrical lenses or thelike to make the irradiated image rectangular are commerciallyavailable.

Also, assuming that the status perpendicular to the irradiation portionis 0°, the closer this angle α is to 90°, the more the bead cuttingshape observed with the later-described camera 230 is expanded in thepipe axial direction, but at the same time increases the effects ofdistance fluctuations between the measurement head 250 and the innerface of the pipe, so the present embodiment uses α=70° as a suitablevalue taking the balance of both into consideration, based on priorexperiments.

The camera 230 observes the irradiation image of the slit lightirradiated onto the bead cutting portion from an angle β as to thecross-section of the electric resistance welded pipe 210, and ITVs orcameras using semiconductor devices such as CCD or CMOS which are widelyused in industrial fields can be used. Also, a commercially-availablecamera lens may be used for the lens 232 for image formation by thecamera, but a band-pass filter having a passage wavelength band matchingthe wavelength of the light source in order to eliminate unnecessarylight such as background light or the like from the optical cuttingimage, and a heat-ray cut filter or the like for preventing damage tothe image-taking surface of the camera and the lens from radiant heat,should be provided as necessary.

The measurement head 250 is preferably a sealed structure for protectingthe optical equipment such as the camera 230, light source 220, lens232, etc., within from heat and water and the like, and in this case, apreferably configuration has windows 252 and 254 for only the slit lightand camera field of view portions, respectively.

The position angle of the camera 230 is preferably such that (α+β) isgenerally 90°, with the number of pixels of the camera and the field ofview being determined based on the width of the bead portion and thenecessary resolution. With the present invention, the slit lightirradiation angle from the light source 220 is α=70°, the image-takingangle is β=30°, the range of the field of view is 25 mm wide and 20 mmhigh, and the number of pixels is 1300 horizontally by 1000 vertically,as a suitable value. Thus, the height-wise resolution is20/1000*cos(70°)/sin(70°+30°)=0.0069 mm. Also, the width-wise resolutionis 25/1300=0.0192 mm, so the bead cutting state can be monitored with aresolution of 20 μm in the width direction (circumferential direction)and 7 μm in the height direction (pipe axial direction).

Also, it is needless to say that the light source 220 and camera 230should be positioned such that the optical axes thereof intersectprecisely over the bead cutting portion, and further, the plane formedby the axial axes of the light source 220 and camera 230 even morepreferably contains the direction of progression of the electricresistance welded pipe 210, i.e., the center axis of the pipe. Thereason is that this arrangement of the light source and the cameraallows the optical cutting image on the inner face of the pipe to behorizontally symmetrically taken with regard to a virtual center lineextending in the Y-axial direction on the optical cutting image.

Further, the light source 220 and the camera 230 may be fixed to themeasurement head 250 in an inclined state as shown in FIG. 16, or may bedisposed so that their optical axes are both parallel to the centralaxis within the electric resistance welded pipe to reduce the size ofthe device, with the angle of the optical axis being changed by thereflection mirror 236.

Next, the configuration of the components of the control device 270 willbe described. The image data conversion circuit 272 converts each pixelof image signals output form the camera 230 into luminance data andoutputs, and an image board (frame-grabber) widely commerciallyavailable in recent years, which is compatible with the camera 230, canbe used.

The thinning processing circuit 275 is for performing thinningprocessing of the slit light image within the acquired picture. Eitherconventionally known thinning processing means, or the thinningprocessing method proposed here by the Inventors, may be used.

The image synthesizing circuit 281 is for overlaying the slit lightimage picture subjected to thinning processing as described above, andthe original optical cutting image (original image picture) output fromthe image data conversion circuit. Specifically, the image synthesizingcircuit 281 performs computation such as addition of values of pixels onthe same coordinates in the image, obtaining the logical OR, overwritinga thinning line alone on the original image picture, and so forth.

Next, the operations of the present embodiment will be described.

FIG. 17 is an optical cutting image of a cut bead observed with thedevice according to the present embodiment at the time of manufacturingthe electric resistance welded pipe 210, and FIG. 18 is the thinningprocessing results of the optical cutting image shown in FIG. 17. Here,recessed notches occur in the thinning results as indicated by thearrows in FIG. 18, due to scattered light noise at the circled portionsin FIG. 18. This can be told from the output of the present embodimentbeing as shown in FIG. 19. According to the present invention, theoriginal image picture and the thinning results can both be confirmed asshown in FIG. 19, so mistaking such notches due to scattered light noisefor cutting steps can be avoided.

Fourth Embodiment

FIG. 20 is a block diagram illustrating the configuration of thecomputation circuit group within the control device 270 according toanother embodiment of the present invention. The unshown bead trimmer212 and the measurement head 250 to be mounted thereupon are of the sameconfiguration as those in the first embodiment, so description thereofwill be omitted.

Also, in FIG. 20, the same image data conversion circuit 272 andthinning processing circuit 275 as the first embodiment may be used.

The SN ratio detecting circuit 277 is for calculating the ratio betweenthe luminance of the optical cutting line image and the luminance of aportion outside of the optical cutting line image, at the same Xcoordinate in the image at the time of performing thinning processing,for each X coordinate, and can be realized by combining a known maximumvalue searching circuit and dividing circuit.

Also, the thinning circuit 288 is for coloring each pixel on the thingline portion in the thinning image according to the SN ratio at each Xcoordinate, output by the SN ratio computation circuit, and may becolored with grayscale or an arbitrary color order. A preferred exampleof the present embodiment is arranged with colors corresponding to theSN ratio being assigned in 16 steps, as shown in Table 1. In Table 1,intermediate colors of commonly-known color names are frequently used,so the colors are also listed in the RGB luminance format, as well.

TABLE 1 SN ratio Lower limit Upper limit Color RGB luminance Lower 1.0Blue (0, 0, 255) 1.0 1.3 Blue-green (0, 128, 255) 1.3 1.7 Green (0, 255,0) 1.7 2.0 (36, 255, 0) 2.0 3.0 (73, 255, 0) 3.0 5.0 (109, 255, 0) 5.08.0 Yellow-green (146, 255, 0) 8.0 10.0 (182, 255, 0) 10.0 14.0 (219,255, 0) 14.0 16.0 Yellow (255, 255, 0) 16.0 20.0 (255, 159, 0) 20.0 25.0(255, 127, 0) 25.0 30.0 (255, 95, 0) 30.0 40.0 (255, 63, 0) 40.0 HigherRed (255, 0, 0)

Next, the results of implementing the present embodiment will bedescribed.

FIG. 21 is an optical cutting image of a cut bead observed with thedevice according to the present embodiment while manufacturing theelectric resistance welded pipe 210, and FIG. 22 and FIG. 23 are theresults of thinning processing of the optical cutting image. Now, theportions in FIG. 22 indicated by the arrows have marked protrusions inthe thinning results, which are portions exhibiting abnormal values inthe thinning processing due to the luminance of the slit light at thisportion being very small, but these cannot be recognized withconventional lines alone being displayed. Conversely, FIG. 23 is athinning image output from the thinning circuit according to the presentembodiment, which shows that the SN at the portions corresponding to thecircled portions in FIG. 22 is at a minimal level (blue or blue-green)by the color of the thinning image. Accordingly, erroneously recognizingthe cutting shape of this portion was prevented.

Fifth Embodiment

FIG. 24 is a block diagram illustrating the configuration of thecomputation circuit group within the control device 270 of yet anotherembodiment according to the present invention. The unshown bead trimmer212 and the measurement head 250 to be mounted thereupon are of the sameconfiguration as those in the first embodiment, so description thereofwill be omitted.

Also, in FIG. 24, the same image data conversion circuit 272 andthinning processing circuit 275 as the first embodiment may be used, andthe same SN ratio detecting circuit 277 and thinning circuit 288 as thesecond embodiment may be used.

Next, the results of implementing the present embodiment will bedescribed.

FIG. 25 is an optical cutting image of a cut bead observed with thedevice according to the present embodiment while manufacturing theelectric resistance welded pipe 210, and FIG. 26 is the results ofthinning processing of the optical cutting image shown in the opticalcutting image in FIG. 25. Now, the portion in FIG. 26 indicated by thearrow has irregularities in the thinning results, which is a portionexhibiting abnormal values in the thinning processing due to theluminance of the slit light at this portion being very small, besideseffects of scattering noise, but these cannot be recognized withconventional lines alone being displayed. Conversely, FIG. 27 is athinning image output from the thinning circuit according to the presentembodiment, which shows that the SN at the portion corresponding to thecircled portion in FIG. 26 is at a minimal level (blue or blue-green) bythe color of the thinning image, and that has departed from the originaloptical cutting line image. Accordingly, mistaking this portion for acutting step was prevented.

While the above embodiments have been described using an RGB system as asuitable example of coloring the optical cutting line, being is the mostcommon notation method in the field of computer graphics, the presentinvention is by no means restricted to this, and it is needless to saythat other color notation methods such as CYMK may be used to obtain thesame advantages.

Also, with the above-described embodiments, it is needless to say thatall or part of the thinning circuit 275, the SN ration detection circuit277, and the remaining image processing computation group, within thecontrol device 270, may be realized by software, programs in ROM, etc.,within a digital computer.

Sixth Embodiment

FIG. 31 is a schematic diagram illustrating an example of an equipmentconfiguration of a bead detecting device for a electric resistancewelded pipe according to the present invention. In FIG. 31, referencenumeral 320 denotes the electric resistance welded pipe, 301 denotinglight projecting means, 302 denoting image-taking means, 303 denotingprofile calculating device, 304 denoting a profile data processingdevice, and 305 denoting a display device.

FIG. 32 is a configuration diagram illustrating the internalconfiguration of the profile data processing device 304. In FIG. 32,reference numeral 310 denotes a temporary apex calculating circuit, 311denotes a first regression computation circuit, 312 denotes anintersecting point calculating circuit, 313 denotes a first rangecalculating circuit, 314 denotes a second regression computationcircuit, 315 denotes a deviation calculating circuit, and 316 denotes asecond range calculating circuit.

As for the light projecting means 301 in FIG. 31, a slit light sourcewherein light emitted from a light emitting device such as a laser orlamp is converged at a line with a cylindrical lens or the like, or ascanning point light source wherein a light which converges at a pointon an irradiation position is scanned in the width direction using amirror or the like, may be used, but a small-size slit light sourcewherein a light emitting diode (LED) and a lens system are integrated ispreferably used, the width of the short side of the slit is preferablysufficiently smaller than the height of the welding bead, preferably 50μm or smaller. Ultimately, the shape of the portion to be measured iscalculated as a single line by the later-described opticalcross-sectional image processing, so this is not indispensable butshould be as small as practicable.

As for the image-taking means 302, ITV cameras or a PSD (PositionSensitive Device, an optical position detecting device) may be used, buttaking the ease of data conversion to the following image processingdevice, a CCD camera is suitably used. Also, though omitted in FIG. 31,common arrangements may be selected and used for the lens mechanism forforming an image from irradiated light, the aperture diaphragm foradjusting the amount of light received to an appropriate range, theshutter mechanism, and so forth. Now, in the event of using the methodof scanning a point light as the light source, it is needless to saythat there is the need to continuously irradiate light while scanningthe entire range in the width direction at least once. As long as theseconditions are satisfied, and the shapes of the pipe and the bead do notchange while scanning, the case of using slit light and the case ofplane scanning of a point light source are equivalent in the subsequentprocessing of the acquired image, so only the case of using slit lightwill be described in the following, which will suffice as descriptionfor both cases.

The incident angle α of the light projecting means 301 serving as thelight source, and the mounting angle of the image-taking means 302,i.e., the image-taking angle β, is preferably such that (α+β) isgenerally 90°, with the number of pixels and the field of view of thecamera, i.e., the image-taking means 302 being determined based on thewidth of the bead portion and the necessary resolution. As suitablevalues for the present invention, the slit light irradiation angle fromthe light source is α=60°, the image-taking angle is β=30°, the range ofthe field of view is 25 mm wide and 20 mm high, and the number of pixelsis 640 horizontally by 480 vertically. Thus, the width-wise resolutionis 25/640=0.0391 mm, and the height-wise resolution is20/480*cos(60°)/sin(60°+30°)=0.0209 mm, so the bead shape can bemonitored with a resolution of 40 μm in the width direction (pipecircumferential direction) and 20 μm in the height direction (pipe axialdirection).

The profile calculating means 303 is for converting a slit light imageprojected on the pipe surface as shown in FIG. 33 into one line withappropriate image processing means, and further calculating a trueprofile in the wall thickness cross-sectional direction of the pipe,i.e., profile data of the electric resistance welded pipe, based on theslit light image, i.e., a pseudo-cross-sectional profile, from theplacement of the light source and the image-taking means, i.e., fromgeometric calculations of the incident angle α and the image-takingangle β. Generally-known thinning processing may be used for the imageprocessing means here, but the thinning processing means proposed by theInventors here is preferably used. Also, the profile data of the pipe issimple, so the above-described geometric calculation part may be omittedwithout any particular problem for the bead shape detection with is anobject of the present invention.

The following is a description of the components within the profile dataprocessing device 304. With the direction crossing the bead portion(width direction) as the X axis in a pseudo-cross-sectional profileobtained by irradiation of slit light as described above, or a profileof the electric resistance welded pipe, following thinning processing ineither case, the profile can be represented as a data group of heightscorresponding to X coordinates.

In this case, the temporary apex calculating circuit 310 calculates theapex position Xc0 of the welding bead, so a configuration forcalculating the weighted mean (position of the first order moment) ofthe profile data, for example, is sufficient.

This can be performed by multiplying the luminance by the vertical axiscoordinate of pixels indicating the luminance and then adding eachobtained value in the vertical axis direction with regard to a givenwidth-direction (X-axial direction) coordinate, dividing this with thenumber of pixels involved therein so as to obtain an average, furtherobtaining the average values for other width-direction (X-axialdirection) coordinates in the same manner and stringing the averagevalues thereof, and further obtaining the X coordinate exhibiting themaximum value on the vertical axis from these.

Or, more simply, this can be performed by stringing pixels exhibitingthe maximum luminance with regard to a given width-direction (X-axialdirection) coordinate, in the width direction (X-axial direction), andobtaining the X coordinate exhibiting the maximum value on the verticalaxis from these.

Also, the first regression computation circuit 311 is for regression ofthe profile data such as shown in FIG. 34 with a quadratic function, soa configuration for executing known regression computation, preferablyleast-square computation, is sufficient. A first approximation curvewherein the first regression computation circuit 311 has approximatedthe profile data with a quadratic function is shown in FIG. 35.

Here, FIG. 34 uses relative values for the height of the bead shown onthe vertical axis. This means values wherein the geometric part areomitted, with regard to the fact that the above-described geometriccalculation part may be omitted without any particular problem for thebead shape detection which is an object of the present invention sincethe profile data of the electric resistance welded pipe is simple, asdescribed earlier. This understanding holds in the followingdescription.

The intersecting point calculating circuit 312 selects, of the pointswhere the profile data and the first approximation curve intersect, thetwo closest points on the left side and right side of the apex Xc0, asX1 and Xr, respectively, as shown in FIG. 35.

The first range calculating circuit 313 calculates the range of thecoordinates used for the following base pipe regression, based on the X1and Xr calculated by the intersecting point calculating circuit 312, andthe apex Xc0. For example, a suitable example is to calculate R: x<X1′,x>Xr′ based on the 3:2 externally dividing point of the apex andintersecting points.X1′=(3×1−Xc0)/2Xr′=(3×r−Xc0)/2

This external dividing ratio should be decided as appropriate, takinginto consideration the smoothness of the slope of an average bead, basedon experience, for example.

A configuration wherein the second regression computation circuit 314performs least-square polynomial regression computation in the range Rfor x that has been calculated as described above, as with the firstregression computation circuit, is sufficient. However, it should benoted that the polynomial used for calculations at the second regressioncomputation circuit 314 is a polynomial of an even degree quadratic orhigher, and preferably is a quartic or higher polynomial. This yieldsthe second approximation curve. This second approximation curve isextrapolated into the region X1′≦x≦Xr′ outside of the range R for theabove-described x, as well.

The deviation calculating circuit 315 is for calculating the deviationbetween the second approximation curve output by the second regressioncomputation circuit and the profile data of the electric resistancewelded pipe, over the entirety of X coordinates where profile data ofthe electric resistance welded pipe exists (“entirety” meaning withinthe image field of view as an optical cutting image), and can beconfigured of a polynomial computation circuit and a subtractioncircuit.

The second range calculating circuit 316 then calculates the range wherethe output of the deviation calculating circuit 315 exceeds thepredetermined threshold value and outputs the portion of this rangecontaining the apex Xc0 as a temporary existence range for the bead, andcan be configured of a threshold circuit and a comparator circuit.

The operations of the present embodiment will now be described withreference to data.

The optical cutting image obtained by the light projecting means 301irradiating slit light onto the surface of the pipe and taking an imagethereof with the image-taking device 302 is as shown in FIG. 33, and theprofile data of the electric resistance welded pipe including the beadportion calculated by the profile calculating means 303 from thisoptical cutting image that has been subjected to thinning processing isas shown in FIG. 34. The temporary apex calculating circuit 310calculates the apex by a technique such as maximum value computation,weighted mean (center of gravity computation), etc., with regard to thisprofile data. The Xc0 marked in FIG. 34 is the apex position of the beadthus calculated.

The first regression computation circuit 311 performs least-squareregression computation by the quadratic expression of the entireprofile, consequently outputting a quadratic function as shown in FIG.35. The X1, Xr, X1′, and Xr′ marked in FIG. 35 in the same way arepositions of X coordinates calculated by the intersecting pointcalculating circuit 312 and range calculating circuit 313, as describedabove.

The second regression computation circuit 314 calculates the secondapproximation curve for the profile data regarding the range of the Xcoordinates set by the range calculating circuit 313. In thisembodiment, the quartic degree was selected as a suitable example forregression. The second approximation curve obtained as a result is asshown in FIG. 36 by the heavy line.

The deviation calculating circuit 315 calculates the deviation e(x)between the heavy line in FIG. 36 and the profile data of the electricresistance welded pipe, and the results thereof are obtained as shown inFIG. 37.

The second range calculating circuit 316 searches for ranges whereinthis deviation e(x) exceeds a threshold value set beforehand, and ofthese, calculates a range of X coordinates including the apexcoordinates Xc0. A threshold value of 0.05 was used as a suitableexample in the present embodiment. The results thereof indicate therange marked by the arrows in FIG. 37.

In order to confirm the validity of the present invention, a comparisonwas made between a photograph of the bead taken with an arrangement withthe same light projecting means and image-taking means as the presentembodiment wherein light emission from the light source was stopped andthe exposure time extended, and the bead shape image output according tothe present invention. The results are as shown in FIG. 38, wherein itcan be understood that the photograph matches the calculated bead shape(shown at the bottom of FIG. 38) very well.

With the above-described embodiment, it is needless to say that all orpart of the internal configuration circuits of the profile calculatingdevice 303 and profile data processing device 304 may be realized bysoftware or programs in ROM, within a digital computer. Of course, theobject of application of the present invention is not restricted tosteel pipe, and may be other metal pipes, such as copper, aluminum, andso forth.

FIG. 40 is a schematic diagram illustrating a configuration example of aelectric resistance welded pipe bead shape detecting device according tothe present invention. In FIG. 40, reference numeral 420 denotes theelectric resistance welded pipe, with 401 denoting light projectingmeans, 402 denoting image-taking means, 403 denoting bead shapecalculating means, 404 denoting a data processing device, and 405denoting a display device.

As for the light projecting means 401, a slit light source wherein lightemitted from a light emitting device such as a laser or lamp isconverged on a plane with a cylindrical lens or the like, or a scanningpoint light source wherein a light which converges at a point on anirradiation position is scanned in the width direction using a mirror orthe like, may be used, but a small-size slit light source wherein asemiconductor device (LED) and a lens system are integrated ispreferably used, the width of the short side of the slit is preferablysufficiently smaller than the height of the welding bead, preferably 50μm or smaller. Ultimately, the shape of the portion to be measured iscalculated as a single line by the later-described optical imageprocessing, so this is not indispensable.

As for the image-taking means 402, ITV cameras or a PSD (PositionSensitive Device, an optical position detecting device) may be used, buttaking the ease of data conversion to the following image processingdevice, a CCD camera is suitably used. Also, though omitted in thedrawings, common arrangements may be selected and used for the lensmechanism for forming an image from irradiated light, the aperturediaphragm for adjusting the amount of light received to an appropriaterange, the shutter mechanism, and so forth. Now, in the event of usingthe method of scanning a point light as the light source, it is needlessto say that there is the need to continuously expose while irradiatingthe entire range in the width direction at least once. As long as theseconditions are satisfied, and the shapes of the pipe and the bead do notchange while scanning, the case of using slit light and the case ofplane scanning of a point light source are equivalent in the subsequentprocessing of the acquired image, so only the case of using slit lightwill be described in the following, which will suffice as descriptionfor both cases.

The incident angle α of the light projecting means 401, and the mountingangle β of the image-taking means 402, is preferably such that (α+β) isgenerally 90°, with the number of pixels and the field of view of thecamera, being determined based on the width of the bead portion and thenecessary resolution. As suitable values with the present invention, theslit light irradiation angle from the light source is α=60°, theimage-taking angle is β=30°, the range of the field of view is 25 mmwide and 20 mm high, and the number of pixels is 640 horizontally by 480vertically. Thus, the width-wise resolution is 25/640=0.0391 mm, and theheight-wise resolution is 20/480*cos(60°)/sin(60°+30°)=0.0209 mm, so thebead shape can be monitored with a resolution of 40 μm in the widthdirection (pipe circumferential direction) and 20 μm in the heightdirection (pipe axial direction).

The bead shape calculating means 403 are for taking the slit light imageas one line with suitable image processing means, and calculating a beadshape (profile) by geometric calculations determined by the positioningof the light projecting means 401 and the image-taking means 402. Now, aprofile refers to the outline shape on the inner face or output face ofthe electric resistance welded pipe, and the shape data of the pipesurface including the bead portion is from a section thereof.Generally-known thinning processing may be used for the image processingmeans here, but the thinning processing means proposed by the Inventorshere is preferably used.

The internal configuration of the data processing device 404 is shown inFIG. 41, comprising a apex position setting circuit 410, a bead rangesetting circuit 411, a bead shape approximation circuit 412, a base pipeshape approximation circuit 413, a bead range re-setting circuit 414,and a features calculating circuit 415.

The following is a description of the components of the data processingdevice 404.

The apex position setting circuit 410 sets the apex position of the beadfrom shape data of the pipe surface including the bead portioncalculated as described above. An arrangement may be made wherein anoperator judges and manually inputs the apex position of the bead fromthe shape data of the pipe surface containing the bead portion, but amore preferable arrangement is to obtain a position indicating themaximum height value in the shape data of the pipe surface containingthe bead portion. Further, this can by calculated with additionprocessing by weighted mean computation or the like.

The bead range setting circuit 411 sets a bead range from shape data ofthe pipe surface including the bead portion, calculated as describedabove. An arrangement may be made wherein an operator judges the beadrange from the shape data of the pipe surface containing the beadportion and manually inputs the boundaries at the left and right edgesof the bead portion, and sets the region equivalent to the portionbetween left and right boundaries as the bead range, or an arrangementwherein the slope position is detected based on difference in adjacentshape data, such as disclosed in Patent Document 3, but a morepreferable arrangement is to divide a preset bead width into two halvescentered on the bead apex position output from the apex position settingcircuit 410, or to set following the method disclosed in the electricresistance welded pipe bead shape detecting method which the Inventorspropose here.

The bead shape approximation circuit 412 divides the bead range which isset as described above into the left side of the apex x₁<x<x_(c) and theright side of the apex x_(c)<x<x_(r), approximates the shape of the beadportion in each range with a predetermined function, and determines thefunction with regard to the shape of the left and right portions of thebead portion. A preferred method thereof will be described in thesection on the operations of the present embodiment, later.

The base pipe shape approximation circuit 413 is for approximating theshape data of the bead range thus set with pipe surface shape data,wherein the shape data of the bead range is removed from the shape dataof the pipe surface including the bead portion, and a function of apredetermined form such as a power function or the like, and specificparameters such as the coefficients of the functions are calculated. Apreferred method thereof will be described in the section on theoperations of the present embodiment, later.

The bead range re-setting circuit 414 is for re-recognizing thepositions where the values of the approximation functions of thethus-determined left and right bead shape and the approximation functionof the base pipe shape intersect as the boundary positions between thebead portion and the base pipe position, and can be configured from afunction value computation circuit and a comparator.

The features calculating circuit 415 is for calculating the bead width,height, left and right slope angles, and unevenness between the boundarybetween the left and right bead portions and the base pipe portion,based on the thus-calculated bead range, apex position, approximationfunctions for the left and right bead shapes, approximation function forthe base pipe shape, and shape data of the pipe surface including thebead portion.

The display device 405 displays the features of the bead shape detectedby the features calculating circuit 415. While each of the values may beperiodically updated and displayed as numbers or bar charts, apreferable arrangement is to display the shape data of the pipe surfaceincluding the bead portion and the features of each as a time chart.

Also, an arrangement may be made wherein the output for the featurescalculating circuit 415 is output to an unshown recorder or businesscomputer or the like by an unshown communication port or external outputcircuit, at appropriate time intervals, so as to accumulate data.

Next, the operations of the present invention will be described.

FIG. 42 is an optical cutting image of the slit light source 401 servingas the light projecting means covering the range of the pipe surfaceincluding the bead portion, taken with the image-taking means 402, andthe results of subjecting this to thinning processing with the beadshape calculating means 403 and converting into coordinates on thedisplay device 405 is the shape data of the pipe surface including thebead portion such as shown in FIG. 43. The arrows marked in FIG. 43indicate the bead range calculated by the apex position setting circuit410 and the bead range setting circuit 411, and the x coordinate at theapex position. In the present embodiment, calculation of the apexposition uses a value calculated as being x_(c)=−0.0781 from theweighted mean.

(Mathematical Expression 1)

$x_{c} = \frac{\sum\limits_{i = i_{L}}^{i_{R}}{x_{i} \cdot z_{i}}}{\sum\limits_{i = i_{L}}^{i_{R}}z_{i}}$of the shape data of the pipe surface including the bead portion (x_(i),z_(i)) (i=i_(L), . . . , i_(R)), having a predetermined bead range asthe domain thereof, as to the data row of the shape data of the pipesurface including the bead portion (x_(i), z_(i)) (i=0, . . . , N−1).The bead range was set atx _(L) =x _(c) −W ₀/2=−2.0781 mmx _(R) =x _(c) +W ₀/2=1.9219 mm

using the general bead width W₀=4 mm that had been set beforehand. Here,i_(L) and i_(R) are shape data addresses for the left edge and rightedge of the bead range. Also, the i_(c) used below is an address for ashape data row equivalent to the x_(c) obtained as described above.

The bead shape approximation circuit 412 calculates a function f_(L)(x)which minimizes the following E_(L) and E_(R) with regard to the lefthalf of the bead thus set (from the left side boundary x=x_(iL) to theapex x=x_(ic)), and the right half thereof (from the apex x=x_(ic) tothe right side boundary x=x_(iR)).

(Mathematical Expression 2)

${E_{L} = \left. {\sum\limits_{i = i_{L}}^{i_{c}}\left( {z_{i} - {f_{L}(x)}} \right)^{2}}\rightarrow\min \right.},{E_{R} = \left. {\sum\limits_{i = i_{c}}^{i_{R}}\left( {z_{i} - {f_{R}(x)}} \right)^{2}}\rightarrow\min \right.}$

Now, the processing which will be described below is the same for theleft half and the right half, so from here on, the symbols and so forthwill be described for only the left half side of the bead portion,representatively. Also, circular arcs, polynomials, etc., may be usedfor approximation functions for the shape data at the left side and theright side of the bead portion, but with the present embodiment, anaggregate expression of line segments is used as a preferred example, asfollows.

(Mathematical Expression 3)

${f_{L}(x)} = \left\{ \begin{matrix}{{a_{L1}x} + b_{L1}} & {x_{i_{L}} \leq x < x_{i_{P1}}} \\\vdots & \vdots \\{{a_{Lj}x} + b_{Lj}} & {x_{i_{p_{j - 1}}} \leq x < x_{i_{pj}}} \\\vdots & \vdots \\{{a_{L1}x} + b_{L1}} & {x_{i_{p_{n - 1}}} \leq x < x_{i_{c}}}\end{matrix} \right.$

wherein n is the number of line segments, and i_(P1), . . . , i_(Pn) areaddresses of concatenation points which satisfy i_(L)<i_(P1)< . . .<i_(Pj)< . . . <i_(Pn−1)<i_(c). The number of concatenation points,i.e., the number of line segments may be set arbitrarily, but takingcomputation time into consideration, n=2 was set for the presentembodiment. Accordingly, there is one concatenation point with thepresent embodiment, so in the following description, p1 may be writtenwith the p and indices omitted.

Now, in this case, the least value of E_(L) is to be solved regardingthe five parameters of a_(L1), b_(L1), a_(L2), b_(L2), and x_(p1), inorder to calculate f_(L)(x), which can be calculated by dividing intothe following steps.

(1) First, x_(p) is fixed, and a_(L1), b_(L1), a_(L2), and b_(L2) arecalculated for this case. In this case, this is linear least-squareregression as to the data set (x, z), and can be algebraically obtainedas follows.

(Mathematical Expression 4)

$\begin{matrix}{{a_{L1} = \frac{{\sum\limits_{i = i_{L}}^{i_{p}}{1{\sum\limits_{i = i_{L}}^{i_{p}}{x_{i}z_{i}}}}} - {\sum\limits_{i = i_{L}}^{i_{p}}{x_{i}{\sum\limits_{i = i_{L}}^{i_{p}}z_{i}}}}}{{\sum\limits_{i = i_{L}}^{i_{p}}{x_{i}^{2}{\sum\limits_{i = i_{L}}^{i_{p}}1}}} - \left( {\sum\limits_{i = i_{L}}^{i_{p}}x_{i}} \right)^{2}}},} & {b_{L1} = \frac{{- {\sum\limits_{i = i_{L}}^{i_{p}}{x_{i}{\sum\limits_{i = i_{L}}^{i_{p}}{x_{i}z_{i}}}}}} + {\sum\limits_{i = i_{L}}^{i_{p}}{x_{i}^{2}{\sum\limits_{i = i_{L}}^{i_{p}}z_{i}}}}}{{\sum\limits_{i = i_{L}}^{i_{p}}{x_{i}^{2}{\sum\limits_{i = i_{L}}^{i_{p}}1}}} - \left( {\sum\limits_{i = i_{L}}^{i_{p}}x_{i}} \right)^{2}}} \\{{a_{L2} = \frac{{\sum\limits_{i = i_{p}}^{i_{c}}{1{\sum\limits_{i = i_{p}}^{i_{c}}{x_{i}z_{i}}}}} - {\sum\limits_{i = i_{p}}^{i_{c}}{x_{i}{\sum\limits_{i = i_{p}}^{i_{c}}z_{i}}}}}{{\sum\limits_{i = i_{p}}^{i_{c}}{x_{i}^{2}{\sum\limits_{i = i_{p}}^{i_{c}}1}}} - \left( {\sum\limits_{i = i_{p}}^{i_{c}}x_{i}} \right)^{2}}},} & {b_{L2} = \frac{{- {\sum\limits_{i = i_{p}}^{i_{c}}{x_{i}{\sum\limits_{i = i_{p}}^{i_{c}}{x_{i}z_{i}}}}}} + {\sum\limits_{i = i_{p}}^{i_{c}}{x_{i}^{2}{\sum\limits_{i = i_{p}}^{i_{c}}z_{i}}}}}{{\sum\limits_{i = i_{p}}^{i_{c}}{x_{i}^{2}{\sum\limits_{i = i_{p}}^{i_{c}}1}}} - \left( {\sum\limits_{i = i_{p}}^{i_{c}}x_{i}} \right)^{2}}}\end{matrix}$

(2) The approximation error E(x_(p)) in the case of x=x_(p) iscalculated using the a_(L1), b_(L1), a_(L2), and b_(L2) calculatedabove.

(Mathematical Expression 5)

$\begin{matrix}{{E\left( x_{p} \right)} = {\sum\limits_{i = i_{L}}^{i_{R}}\left( {z_{i} - {f_{L}(x)}} \right)^{2}}} \\{= {{\sum\limits_{i = i_{L}}^{i_{p}}\left( {z_{i} - {a_{L1}x_{i}} - b_{L1}} \right)^{2}} + {\sum\limits_{i = i_{p}}^{i_{R}}\left( {z_{i} - {a_{L2}x_{i}} - b_{L2}} \right)^{2}}}}\end{matrix}$

(3) The computations in (1) and (2) above are performed for all.

(Mathematical Expression 6)i _(p) ε[i _(L) ,i _(R)]

and the x_(ip) where E(x_(ip)) is the smallest is the concatenationpoint to be obtained.

(4) the f_(L)(x) corresponding to the x_(ip) calculated above is takenas the approximation function of the shape of the pipe surface includingthe bead portion.

(5) The same computation of (1) through (4) above is performed withi_(c) instead of i_(L) and i_(R) instead of i_(c) in the same way, forthe approximation function of the bead shape to the right side of theapex point.

FIG. 44 is an example of a diagram plotting the relation between eachx_(p) and the approximation error E(x_(p)), with regard to, of the shapedata of the pipe surface including the bead portion shown in FIG. 43,the shape data to the left side of the apex position, wherein theminimal value is at x_(p)=−0.7031, as shown in the drawing, andaccordingly, the approximation function of the bead shape at the leftside can be determined as being.

(Mathematical Expression 7)

${f_{L}(x)} = \left\{ \begin{matrix}{{1.0586x} - 3.76155} & {{- 2.0781} \leq x < {- 0.7031}} \\{{0.12345x} + 6.789} & {{- 0.7031} \leq x < 0.07813}\end{matrix} \right.$

Of the shape data of the pipe surface including the bead portion, thebase pipe shape approximation circuit 413 calculates the approximationfunction f_(p)(x) with regard to the range excluding the bead portion.Though a circle or ellipse may be used for this approximation functionf_(p)(x), a power function, and an even degree polynomial, quadratic orhigher, is preferably used as the approximation curve.

To support this, FIG. 45 is a chart illustrating the relation betweenthe degree of a polynomial and the RMS (root-mean-square) ofapproximation error, in a case of regression of the upper half curve ofa circle with quadratic, quartic, sextic, and octic polynomials,indicating that a polynomial of an even degree quadratic or higher, andpreferably a quartic or higher polynomial, can perform regression of theshape of the ellipse with sufficient precision. Accordingly, with thepresent embodiment, approximation is performed with a quartic function.Specifically, with regard to the coordinates range.

(Mathematical Expression 8)xεD={[x ₀ ,x _(L) ]∪[x _(R) ,x _(N)]}

of the shape data of the pipe surface including the bead portion shownin FIG. 43, the coefficient for the quartic function.

(Mathematical Expression 9)

$J = \left. {\sum\limits_{x \in D}\left\{ {z - {f_{p}(x)}} \right\}^{2}}\rightarrow\min \right.$

wherein the sum of squares of error defined as

(Mathematical Expression 10)z=f _(p)(x)=a ₀ +a ₁ x+a ₂ x ² +a ₃ x ³ +a ₄ x ⁴is minimal, is calculated. This can be solved algebraically, and iscalculated by(Mathematical Expression 11)

$\begin{bmatrix}a_{0} \\a_{1} \\a_{2} \\a_{3} \\a_{4}\end{bmatrix} = {{{inv}\left( {\sum\limits_{x \in D}\begin{bmatrix}1 & x & x^{2} & x^{3} & x^{4} \\x & x^{2} & x^{3} & x^{4} & x^{5} \\x^{2} & x^{3} & x^{4} & x^{5} & x^{6} \\x^{3} & x^{4} & x^{5} & x^{6} & x^{7} \\x^{4} & x^{5} & x^{6} & x^{7} & x^{8}\end{bmatrix}} \right)}{\sum\limits_{x \in D}\begin{bmatrix}z \\{zx} \\{zx}^{2} \\{zx}^{3} \\{zx}^{4}\end{bmatrix}}}$

wherein inv(A) represents the inverse matrix of the matrix A. With thepresent embodiment, calculating the above Expression yieldedf _(p)(x)=1.60921+0.055776x−0.02129x ²−0.00015x ³+0.000057x ⁴.

The bead range re-setting circuit 414 calculates the intersecting pointsof the left and right bead shape approximation functions f_(L)(x) andf_(R)(x) calculated as described above with the base pipe shapeapproximation function f_(p)(x), and outputs the region corresponding tobetween the calculated left and right intersecting points as a new beadrange (x_(L)′, x_(R)′)

The f_(L)(x), f_(R)(x), and f_(p)(x) calculated in the presentembodiment are as shown in FIG. 46, and the bead range re-settingcircuit output x_(L)′=−2.2266, and x_(R)′=3.5938. The dashed lineplotted in FIG. 46 is the shape data of the pipe surface including thebead portion, the same as that shown in FIG. 43.

The features calculating circuit 415 calculates the bead height H, widthW, slope angles θ_(L) and θ_(R) of the left and right bead portions, andthe unevenness Δ between the left and right bead portion boundaries,from the thus-calculated bead range, apex position, approximationfunctions for the left and right bead shapes, approximation function forthe base pipe, and the shape data of the pipe surface including the beadportion.

As preferred determination methods for the features, the presentembodiment performs calculations following the following definitions.

-   -   Bead width W: the spacing in the pipe circumference direction        between the left and right bead boundaries output from the bead        range re-setting circuit.    -   Bead height H: the difference in values between the shape data        of the pipe surface including the bead portion at the bead apex        position and the approximation function of the base pipe shape.    -   Bead slope angles θ_(L) and θ_(R): the arctangent of each        inclination defined by differential functions at the boundary        between the left and right approximation functions of the bead        shapes and the approximation function of the base pipe.    -   Unevenness Δ between the left and right boundaries between the        bead portion and the base pipe: the difference in values between        the approximation functions of the left and right bead shapes at        the left and right bead boundary positions output by the bead        range re-setting circuit 414 and the approximation function of        the base pipe shape.

The method for calculating the bead slope angle will be described infurther detail. Describing the procedures for calculating the left-sidebead slope angle, the inclination vectors V_(P) and V_(L) at x=X_(iL) ofthe approximation function f_(p)(x) of the base pipe shape and theapproximation function f_(L)(x) of the left side bead shape are

(Mathematical Expression 12)v _(p)=(1,f _(p)′(x _(L)))=(1,a ₁+2a ₂ x _(L)+3a ₃ x _(L) ²+4a ₄ x _(L)³)=(1,)v _(L)=(1,f _(L)′(x _(L)))=(1,a _(L1))=(1,)

so the angle θ_(L) formed by these two is calculated by

(Mathematical Expression 13)

$\begin{matrix}{{\cos\;\theta_{L}} = {\frac{v_{L} \cdot v_{p}}{{v_{L}}{v_{p}}} = \frac{1 + {{f_{p}^{\prime}\left( x_{L} \right)}{f_{L}^{\prime}\left( x_{L} \right)}}}{\sqrt{1 + \left( {f_{p}^{\prime}\left( x_{L} \right)} \right)^{2}}\sqrt{1 + \left( {f_{L}^{\prime}\left( x_{L} \right)} \right)^{2}}}}} \\{= \frac{1 + {\left( {a_{1} + {2a_{2}x_{L}} + {3a_{3}x_{L}^{2}} + {4a_{4}x_{L}^{3}}} \right)a_{L}}}{\sqrt{1 + \left( {a_{1} + {2a_{2}x_{L}} + {3a_{3}x_{L}^{2}} + {4a_{4}x_{L}^{3}}} \right)^{2}}\sqrt{1 + a_{L}^{2}}}}\end{matrix}$Calculations are performed in the same way for θ_(R), as well.

According to such definitions, the following was calculated with thepresent embodiment.

Bead width (mm): W=x_(R′)−x_(L′)=5.8204

Bead height (mm): H=Z(x_(c))−f_(p)(x_(c))=2.9150

Slope angle of bead at left side (deg) θ_(L)=38.335

Slope angle of bead at right side (deg) θ_(R)=21.392

Unevenness between left and right bead boundaries (mm):Δ=|f _(p)(x_(L))−f _(p)(x _(R))|=0.1576

1. A measurement method for a bead cutting shape of an electric resistance welded pipe, for measuring the shape following cutting a bead generated on the inner face or outer face of an electric resistance welded pipe at a welding portion, said method comprising: a step for obtaining an optical cutting image, by taking an image of slit light irradiated on said bead portion with image-taking means, from an angle different to the irradiation direction of said slit light; a step for obtaining each of maximum luminance in the pipe axial direction at a given width-direction coordinate on said optical cutting image, and maximum luminance in background texture region outside of the irradiation range of said slit light; a step for performing interior division of the maximum luminance of said pipe axial direction and the maximum luminance of said background texture region by a ratio determined beforehand, and setting the obtained luminance as a threshold value; a step for taking a luminance greater than said threshold value and a weighted mean of pipe axial direction coordinates indicating said luminance as pseudo-cross-sectional direction coordinates for said width-direction coordinates and pipe axial direction coordinates; and a step for calculating the bead cutting shape of said electric resistance welded pipe based on a pseudo-cross-sectional shape obtained by stringing pseudo-cross-sectional direction coordinates in the width direction, and a predetermined conversion expression determined from a geometric positional relation of said light source of said slit light, said image-taking means, and said electric resistance welded pipe.
 2. A measurement method for a bead cutting shape of an electric resistance welded pipe, for measuring the shape following cutting a bead generated on the inner face or outer face of an electric resistance welded pipe at a welding portion, said method comprising: a step for obtaining an optical cutting image, by taking an image of slit light irradiated on said bead portion with image-taking means, from an angle different to the irradiation direction of said slit light; a step for taking, in the event that the maximum luminance in the pipe axial direction at a given width-direction coordinate on said optical cutting image is equal to or exceeds a predetermined fixed threshold value, a weighted mean of pipe axial direction coordinates indicating said luminance as pseudo-cross-sectional direction coordinates for said width-direction coordinate and pipe axial direction coordinate; a step for obtaining, in the event that the maximum luminance is less than the predetermined fixed threshold value, each of maximum luminance in the pipe axial direction at a given width-direction coordinate on said optical cutting image, and maximum luminance in background texture region outside of the irradiation range of said slit light; a step for performing interior division of the maximum luminance of said pipe axial direction and the maximum luminance of said background texture region by a ratio determined beforehand, and setting the obtained luminance as a threshold value; a step for taking a luminance greater than said threshold value and a weighted mean of pipe axial direction coordinates indicating said luminance as pseudo-cross-sectional direction coordinates for said width-direction coordinates and pipe axial direction coordinates; and a step for calculating the bead cutting shape of said electric resistance welded pipe based on a pseudo-cross-sectional shape obtained by stringing pseudo-cross-sectional direction coordinates in the width direction, and a predetermined conversion expression determined from a geometric positional relation of said light source of said slit light, said image-taking means, and said electric resistance welded pipe.
 3. A measurement device for a bead cutting shape of electric resistance welded pipe, said device comprising: a slit light source for irradiating slit light at a given incident angle on a bead portion of an electric resistance welded pipe following cutting; image-taking means for taking an irradiation image of said slit light at a different receiving angle; a first computation circuit for calculating, with regard to the optical cutting image output from said image-taking means, the maximum luminance in the pipe axial direction at a given width-direction coordinate on said optical cutting image, and the pipe axial direction coordinate where said maximum luminance occurs; a second computation circuit for calculating the maximum luminance in background texture region, at a position removed by a predetermined number of pixels or more from a pipe axial direction coordinate where said maximum luminance in said pipe axial direction occurs at a given width-direction coordinate; an accumulation circuit for calculating a luminance which is greater than a threshold calculated following a predetermined computation expression from said first computation circuit and said second output computation circuit, and the weighted mean of pipe axial direction coordinates indicating said luminance; an image reconfiguring circuit for stinging the weighted mean of pipe axial direction coordinates thus calculated to generate a pseudo-cross-sectional shape in the width direction; and a coordinates computation circuit for calculating and displaying the bead cutting shape of said electric resistance welded pipe based on a predetermined conversion expression determined from a geometric positional relation of said slit light source, said image-taking means, and said electric resistance welded pipe.
 4. A measurement device for a bead cutting shape of an electric resistance welded pipe, said device comprising: a slit light source for irradiating slit light at a given incident angle on a bead portion of an electric resistance welded pipe following cutting; image-taking means for taking an irradiation image of said slit light at a different receiving angle; a first computation circuit for calculating, with regard to the optical cutting image output from said image-taking means, the maximum luminance in the pipe axial direction at a given width-direction coordinate on said optical cutting image, and the pipe axial direction coordinate where said maximum luminance occurs; a branch circuit for judging whether or not the maximum luminance in the pipe axial direction at said certain width direction is equal to or greater than a predetermined fixed threshold value; a second computation circuit for calculating the maximum luminance in background texture region, at a position removed by a predetermined number of pixels or more from a pipe axial direction coordinate where said maximum luminance in said pipe axial direction occurs at a given width-direction coordinate; a first accumulation circuit for calculating the weighted mean of pipe axial direction coordinates greater than a threshold obtained by interior division of the maximum luminance in the pipe axial direction at said certain width direction, and the maximum luminance at background texture region, by a predetermined ratio; a second accumulation circuit for calculating said luminance equal to or greater than said predetermined fixed threshold value and the weighted mean of pipe axial direction coordinates indicating said luminance; an image reconfiguring circuit for selecting the output of said first accumulation circuit and said second accumulation circuit thus calculated following output from said branch circuit and stringing said output in the width direction so as to generate a pseudo-cross-sectional shape; and a coordinates computation circuit for calculating and displaying the bead cutting shape of said electric resistance welded pipe based on a predetermined conversion expression determined from a geometric positional relation of said slit light source, said image-taking means, and said electric resistance welded pipe.
 5. An electric resistance welded pipe bead shape detecting method, for detecting the bead shape of an electric resistance welded pipe by the optical cutting method, wherein an image, obtained by a slit light being irradiated or a point light being scanned on a welding portion of an electric resistance welded pipe and an image of the slit light irradiated on the surface of the welding portion or an image of the track of the point light scanned thereupon being taken with image-taking means from an angle different to the irradiation direction of said slit light, subjected to predetermined image processing; said method comprising: a step for calculating coordinates for a temporary bead apex by a predetermined calculation expression from a profile of an electric resistance welded pipe; a step for obtaining a first approximation curve by approximating said profile of said electric resistance welded pipe with a quadratic function; a step for calculating the coordinates for two intersecting points on either side of said temporary bead apex from said profile of said electric resistance welded pipe and said first approximation curve; a step for calculating a temporary existence range of the bead by a predetermined calculation expression from the coordinates of said temporary bead apex, and the coordinates of two intersection points on either side of said temporary bead apex; a step for obtaining a second approximation curve by approximating a base pipe shape excluding the temporary existence range of said bead from said profile of said electric resistance welded pipe with an polynomial expression of a degree which is even and quadratic or higher; and a step for determining, of regions wherein the deviation between said profile of said electric resistance welded pipe and said second approximation curve is greater than a predetermined threshold value, a region containing the coordinates of said temporary bead apex as being the bead.
 6. An electric resistance welded pipe bead shape detecting device, comprising: light projecting means for irradiating a slit light or scanning a point light on a welding portion of an electric resistance welded pipe at a given angle; image-taking means for taking an image of said projected light irradiated on the welding portion by said light projecting means, from an angle different to said given angle; profile calculating means for calculating a profile of said electric resistance welded pipe by subjecting the image obtained from said image-taking means to predetermined image processing; temporary bead apex detecting means for calculating coordinates for a temporary bead apex by a predetermined calculation expression from the profile of said electric resistance welded pipe; first regression computation means for approximating with a predetermined regression expression, with said profile of said electric resistance welded pipe as a quadratic function; intersecting point calculating means for calculating the coordinates for two intersecting points on either side of said temporary bead apex from the output of said first regression computation means and the output of said profile calculating means; first range calculating means for-calculating a temporary existence range of the bead by a predetermined calculation expression from the coordinates of said intersection points and the coordinates of said temporary bead apex; second regression computation means for approximating said profile of said electric resistance welded pipe excluding the temporary existence range of the bead thus calculated, with an polynomial expression of a degree which is even and quadratic or higher; and second range calculating means for outputting, of regions wherein the deviation between output from said second regression computation means is greater than a predetermined threshold value and said profile of said electric resistance welded pipe, a region containing the coordinates of said temporary bead apex as being the bead range. 